There was no plausible ARM SOC that Acer could have used 3 months ago (Exynos 5 is clearly not available in any kind of quantities, no other A15s are shipping even on paper, and anything else would be too slow).
Now, as for the HDD, they were clearly optimizing for a $200 pricepoint. If doing a HDD instead of an SSD was what it takes to get there, clearly that's what they had to do. Or are you suggesting that trying to make a $200 ChromeBook at all was a bad call? Because I have to strongly disagree there -- the main original complaints about ChromeBooks were that they were expensive and had incredibly crappy CPUs. This device took care of both those things. That seems totally worthwhile, even if there were other compromises in there.
(Now, this HP on the other hand looks like a completely unjustifiable device.)
In what way is the Samsung ARM ChromeBook "vaporware"? It seems to be available: http://www.amazon.com/Samsung-XE303C12-A01US-Chromebook-Wi-F...
http://gigaom.com/2012/10/22/intel-v-arm-the-chromebook-perf...
I'd link but the site seems down for me at the moment.
The 11" Acer is also cheaper, starting around $220.
So my conclusion is: really HP ? I'd like to hear from others if the SSD makes up the difference.