WWE has signed many names that don't fit their stereotypical (6'2 220 pounds of muscle) criteria in recent years, especially over the last six months.
I'm told while the success of CM Punk and Daniel Bryan has played a factor recently, Triple H is seen as the underlining factor. Hunter's philosophy regarding talent on the indy scene has changed over the years. While he'd prefer talent to have more muscle, he feels workers that have had success on the indy scene are more dedicated to the business and don't flake out as easy. The enforcement of WWE's Wellness Policy as well as injuries related to PED's, not to mention the negative publicity in the "post-Benoit era," have also been contributing factors to his change of heart.
My source pointed specifically to Punk, Bryan and Dean Ambrose and commented how all three would have been seen as nothing more than "indy guys" just a little over a decade ago. The bottom-line is Hunter is committed to WWE having a deeper talent pool with workers that have talent (and experience) and even Vince McMahon has been more open to it.