Risk vs reward. No offense to Hal, but 25% isn't a very big improvement, and signature verification is something that absolutely must work correctly. Get it wrong and people can lose a lot of money very quickly. Why risk it?
Yes, inprinciple I agree, 25% is not much (I only got 22%). But if Hal's secp256k1Verify code is integrated into pre-0.8.0 it could end up to be inserted in the next 0.8.0 release officially. This means, other people recognize this as an important improvement.
And in the light that the probable bottle-neck is (or just has become) this ECDSA_verify heavily(!), I can understand their decision.
To answer your question "Why risk it?": To not lose more and more potential new users because they are annoyed by the huge real-time necessary to verify the current block chain with the official bitcoin versions.
It seems most people don't see this real danger -- this real-time behaviour might restrict (or even kill) bitcoin usage/spread seriously. :-(
smtp