This is an excellent question.
Your response seems to have a very tenuous grasp on coherency. I'm trying to pull out what you're trying to say. It appears to hinge on the transitive verb "to matter", and I can find only one introductory paragraph where the author uses this verb, and he doesn't say anything objectionable the two times that he uses it:
He says that hardware and software both matter. I find that hard to refute. Then he goes on to say that if you asked him to say which matters more, he'd say software. I'm not surprised that he would say this, since he tends to be a "user experience" guy and I'm willing to grand him this premise for the rest of what he wrote.
Honestly I can't tell what counter-argument you're trying to make. Yes, Google has been successful. It certainly wasn't because of their hardware. Regardless, you're only responding to the setup of the thesis, not the thesis itself.
It's this premise that I find inaccurate. Sure there's open everything, but writing an operating system from scratch to support all this is still hard. Hell, give me one commercial operating system written from scratch in the last decade.
The point is, why do it? Maintaining an operating system is big money. And you can't stop there - you've got to have a full-stack offering - business apps, fun apps, drivers, the whole set. Add to that support, interoperability with the world, backwards compatibility etc. It's a long-term commitment; you can't back out of it that easily.
The risk-to-reward ratio is pretty small; unless you have some earth-shaking innovation up your sleeve, and/or it reinforces/supports your business model significantly.
Heck, there's plenty of good solid starting points. What about BSD? Linux? Android?
The point is you need to end up creating an ecosystem around your offering, which is non-trivial. Even if you do, you may still end up as a niche player. Litl is nice; but how well do you think they'll do against traditional netbooks?
I have a little Exokernel project I devote my Saturdays to, and we'll actually be able to offer a POSIX-compliant libOS, and run anything that Linux does.
Or, there's always the hypervisor route, on desktops anyway.
As for the rest of your post, here is Gruber's thesis statement:
PC makers who want to succeed should create their own OSes
Your statement that "Google succeeds without an OS" does not belong in this argument. First, because Google's success has nothing to do with PC making: That's not their business. Google is an online advertising business. To the extent that the rest of their amorphous, cash-cow-supported business plan has any coherency, it seems to be about using various web and mobile apps to drive advertising traffic, although they also derive a certain amount of revenue from selling software subscriptions and licenses, and of course there's AppEngine. And probably some stuff I've forgotten.
Second, because where Google does have a strategy to venture into the hardware market -- with mobile PCs, marketed as "phones", and perhaps desktop/laptop PCs as well -- the plan seems to be to start out by building an OS, just as Gruber suggests. Google's phone venture is centered around Android. I'm not sure what Chrome OS is all about, but if Google releases a tablet or a laptop it will presumably run Chrome. To the extent that Android and Chrome are or will be successful, these will be points in favor of Gruber's argument.
Finally... Apple's first couple of OS X releases really weren't that successful. Apple survived that, of course, because they still had enough dedicated users of their previously successful OS -- Mac OS 9 -- to tide the business over. And of course that iPod thing didn't hurt -- that bought a lot of time. [1] The success of Mac OS X was a near thing, though. Mac fanboy that I was, I nevertheless abandoned the Mac myself for dual-boot XP/Ubuntu in the early 2000s, and didn't come back until OS X 10.3 or 10.4, and I don't think I was alone.
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[1] The iPod, of course, is successful because of iTunes. Which isn't exactly an OS. But is certainly a software ecosystem, common to all Apple hardware, with a circumventable but nonetheless real form of lock-in, built around what was at the time a superior, unified interface for purchasing music, organizing it, and copying it to your devices. The success of the iPod derives mostly from Apple's custom software for the iPod. People have been cloning the hardware forever. Pundits famously didn't see the iPod coming because other companies had beaten Apple to market with apparently equivalent hardware.
Really?! Now maybe. But five years ago? I have a very hard time believing that.
Right now, with the iPhone and iPod Touch, you don't really need to connect them to a computer at all. When I bought my first iPod in 2003, that was absolutely the case, and all the existing PC software for organizing your music sucked ass. I had to use fucking Musicmatch Jukebox to sync my iPod, and the alternative library programs were even worse.
The release iTunes for Windows was a godsend to me -- sure it's pretty resource hungry and has only gotten moreso, but it's pretty fucking fantastic at just getting the basic library management stuff right. Being able to easily rip to AAC was gravy, as it meant that I no longer had to have some of my albums as lossless (MP3's psychoacoustics shit all over gravelly voices). I switched to a Mac a few years later.
But everyone I know who ever got a iPod absolutely loathed iTunes. iTunes was not the reason, the hardware was. I have seen that change with the iPhone. Of course, no data, just anecdotes.