I've been reading about Guerilla games because i have the same queries as you. It looks like they're an incredibly talented bunch of people, both Sony and Microsoft displayed interest in purchasing them in order to secure their future titles, the failure of Killzone 1 seems to have scared off Microsoft (who were suffering in the console market at that point anyway) but Sony bought them regardless.
I can only think there must be other evidence we don't know of that secured them as such a hot property among the console developers such as a tech demo or previous experience. Sony are excellent at running the hype machine (but often pap at delivering) and i'm sure they'd do this for any of their 1st party developers which is adding to the excitement. They've also got excellent taste in choosing developers to buy or form, examples of which would be media molecule or evolution studios, both of which were unheard of when they were purchased, yet have produced some excellent titles. As i say, there's comething to Guerilla that Sony know but we don't.
But yes, there is something unexplainable that makes Guerilla games into an exciting developer, all they've delivered so far is a pap game and a good handheld game yet nobody seems to be able to get enough of them.