If some were $10 and they were titles that were hard to find new, perhaps.
On one hand, I understand that adding Achievements and other goodies simply isn't possible in most cases because why would, say, Double Fine dedicate a half-dozen to a dozen programmers off of Brutal Legend to work on Psychonauts, especially considering the initial public reaction (ie: *Yawn*). It also doesn't help that retooling the code to include things like Achievements may wreck the already-finished product as it is, requiring additional weeks of retooling and QA. Toss in the fact that they would have to work with MS's BC team to either modify the existing emulator for the game or create a whole new one and that's already eating through most of the profits Double Fine might have seen on an XBOriginals release.
On the other, save for Psychonauts, the other titles are ones I could still buy new. While the price makes sense in comparison to the Live Arcade games, it's still a really hard pill to swallow for most of us gamers.
On my non-existant third hand, back in Pittsburgh it seems that the used game scene ebbs and flows all over the place. When a system launch approached or the next "big title" came out the local stores (EB/GS, The Exchange, etc.) were swamped with old games and systems of every variety. When dead periods showed up people who were trading in everything they had would come back and buy up older titles they either traded in or wanted before. 'Twas a beautiful recycling of games, for certain, but some people would be buying back the same title four or five times over. Maybe MS is hoping to tap into that mentality? Even still, it's digital rather than physical media, so it wouldn't touch upon most of these customers either.
Curiouser and curiouser...personally, I say MS should have left it for a later update, possibly Spring. By that time EB/GS could be getting rid of XBox sections in order to save space, so hopefully the New games become "Used" and much harder to find/easier to acquire. Then MS could have rolled out with the Originals with a launch that's 50 titles strong at $10 a pop, which would have been an interesting enough price with a strong lineup behind it. Something for everyone, as it were.