They've made a lot of those kinds of promises -- they don't often deliver, so parent poster is right to feel uneasy about future support.
It's the other Android manufacturers - Samsung, HTC, etc - and the mobile carriers that approve each OTA update that often don't fulfill their promises.
Maybe it's not Google's fault, but that seems like it's skirting the issue: a year after ICS was announced, something like 7.5% of devices are using it, and now we're moving on to JB. We can sit around and blame Samsung and HTC all day, but Google is the steward company of Android and this fragmentation is a real problem that affects developers. If it's creating a shitty situation for developers, it's creating a shitty situation for users.