Now I certainly don't expect anyone else to be that thorough, but my wife always researches available space and was very disappointed in the Nexus 7 which hit her price point at 8GB but didn't leave enough space for her stuff (and of course no SD card slot which finesses the discussion).
But we can anecdote all we want and not make a lot of progress here. If you believe that you should be able to use every byte of space that is advertised on the box, I'm not going to be able to dissuade you. If you accept that the "actual" space is going to be less than the "advertised" space how do you gauge the risk when you buy? Do you just make assumptions about how much of the advertised space will be available? Do you have some sort of internal metric? 90% good, 10% bad or something like that? Do you ever check that metric pre-purchase?
It's not even something I consider, because I've generally assumed that disk capacities are relatively comparable between manufacturers. So I base it on my current space and whether or not I need more.
I don't think its unreasonable to expect that a consumer should be able to look at the specifications for 2 different products and come away with a decent idea of their capabilities. Or at the very least, not be completely misled.
Seriously, isn't this shit that my grandmother is supposed to be able to purchase? Your nerdish idiosyncrasies don't excuse this sort of anti-consumer behavior. It is crap like this that will have me seemingly forever recommending Apple to people I know, and I hate Apple.
Do you yourself personally do this? Do you actively seek out the available disk space when purchasing a new laptop? I think you are fooling yourself if you think even 2% of people do this when buying a new computer. Namely because its rarely if ever in spec sheet.