It's been reported that it was due to lack of addresses for Newt, don't know about Perry. No further details are known at this time. Whether these were largely from one region or dispersed over all districts, whether someone could have deliberately sabotaged the effort (as has been suggested) is unknown. Of course sabotage rarely happens(we hope).
The other candidates (Bachmann etc)did not even submit signatures. I don't know if they just decided not to submit signatures because they had less than 10,000, or some other reason.
The 2 people who qualified (Romney and Paul)have had previous attempts at running and no doubt knew to take advantage of the 15,000 rule. Since they submitted more than 15,000 signatures they were exempt from verification of things such as addresses, and their qualification is deemed rather than verified.(these rules apparently were well known in advance).
Thank you for the most intelligent post on this thread.