Hotz's hacking may have been a contributing factor for getting OtherOS removed, but it's removal does appear to be a motivation to those behind the more complete hacks that followed (I believe it's mentioned in the video series I linked to). So with a timeline of April 2010 to December 2010, fully exploiting the PS3 security took less than 12 months.

Sure, but I think that's orthogonal. My comment is addressing the OPs original premise. I seriously doubt there were hackers sitting around saying "we'll leave the PS3 alone as long as OtherOS stays supported." While removing OtherOS certainly brought more attention to the platform and accelerated the hacking, I think the reason it took so long for the PS3 to be finally cracked mostly had to do with the complexity of the architecture or other things. I don't think OtherOS was a factor.

As a counterpoint, I offer the xbox 360, which to my knowledge has not been cracked except for DVD firmware hacks and physically altering the device (mod chips).

The conclusion of this is that hackers will not continue to win the DRM battle. Eventually, enough holes will be plugged, where cracking these products becomes so time or cost prohibitive that the product stays closed for it's lifetime.