Actually, I'm not sure there will be a 4.5. Here are a few arguments that have changed since 3 => 3.5.
First, they are going to have a paid DI subscriber base. I could very easily see them releasing "rules upgrades" via the DI. Those who pay for the DI get to gradually convert from 4 => 4.2 => 4.5 => 4.7 => etc. Those who don't pay get to deal with pirated copies of the DI or dwell in happy 4e land.
Second, I think they are starting from a better product. To get to 3e, they had a long way to go from 2e. In fact, they had a major overhaul of most things. Some stuff they got right,other stuff they got wrong. They got enough wrong to warrant a 3.5. However, now they are starting with a darn good game in 3.5. There isn't much major to change. Sure, they'll spread it out to 30 levels. Sure, they'll fix grapple and the like. But I really think the game will largely look like an upgraded 3,5, What that means is that if there are less things being overhauled, there are less things that can really go wrong.
I honestly don't expect an official 4.5 - unless the DI falls flat on its face. If the DI is going and WotC are making more than their share on the $10* per month ... I think the gradual changes and upgrades will likely happen there.
*Or whatever the price happens to be.
But above all else, please read this as speculation. I have no better idea of what is going to happen than you do. Unless, of course, you happen to work for WotC R&D. Then, I actually have a worse idea of what is going to happen than you do!
