Exactly this. It would have seemed pretty presumptuous to ask the Debian project to change the support model that they decided worked for them to support us.

We were also faced with a very large new infrastructure build and we knew we were at the end of the line with Squeeze but Wheezy had't quite yet shipped, which put us in an awkward position.

Debian is a great distribution, but at the time we felt like Ubuntu was the right way to go given the existing support policies.