To answer the original question, here are a few of the reasons:
1) Schaub really got the Falcons coaching staff's attention when he was basically ready to be a the backup in a WCO at the end of his first camp, with an excellent preseason. Yes, he ran something similar in Virginia, but the point is that the Falcons felt comfortable giving him responsibility from day one - usually something reserved for top of the first round QBs. How many rookie QBs were backups last year at the end of camp... Leinart, Cutler, Young and....? exactly.
That first preseason, Jim Mora said:
"Poise. Great decision-making. Mobility for a big man. Accuracy under pressure," Mora said.
2) There's
The game against NE in 2005Schaub had one week to prepare for his first NFL start, and he was more than ready. Yes, the NE secondary was banged up, but still Schaub led two 4th quarter TD drives and converted a two point conversion with less than 5 minutes left to tie the game. You can point to Volek, Garrett, or Fitzpatrick, but anyone who watched those QBs, and watched Schaub that day, can attest to the fact that Schaub showed the bread and butter skills you need to make it in this league, whereas the other 3 looked like backups. You have to go beyond the stats.
3) There's all of the interest Schaub has garnered around the league for the last 2 years. Im not even going to link to all the stories, but it's clear that the book on Schaub around the league is that he's starter quality. Minnesota and Miami among others were looking at making a play for him last year, but neither would give their first, which was Atlanta's asking price. Now, you can say that the whole NFL is just buying into the hype too, but you should just know that its not only people like me on this board, or the Texans front office, that believe that Schaub can be at least an adequate starting QB - the entire league has thought it for a while now.