Question is though, what about support. You have a 3 year old Mac of some flavour and upgrade to this OS, what about issues you may have.
ANother aspect would be that by in effect making this level of OS available to all supported models out there warranty wise, they make life in supporting systems a little bit easier and very likely will drop support for the other older OS's on these models quicker. Again making life in support easier in many ways as well as making developers lives a lot easier. Especialy if they can target toward the a single denominator OS wise and take advantage of all the features without working towards only features common to the previous flavours.
Either way a good move. Though can bet there will be somebody on the older flavour of OS who will have some essentual application that they must have which has issues. But time will tell.
Good move on many levels I'd say by Apple.