Callaway Diablo Edge
Callaway Diablo Octane
Callaway Diablo Tour
I might be forgetting a few but what are the differences?
This isn't a new thing. They have different names, while other companys change the number at the end, like Mizuno's MP or MX lines.
Look at Wilson's Staff blades, MacGregor's Tourney or MT lines, Titleist's Tour Models, Ben Hogan's Apex, and so on. They used the same name for dozens of versions which can vary greatly depending on the year. Some versions are good and some aren't. In Hogan's case, most of their various irons earned an extra nickname in addition to "Apex". There are charts to find and date your particular year of Apex. Don't even try to date your 1960s or 1970s MacGregors without having an expert on hand. Looking at their website it seems Titleist made relatively few different sets of blades for quite a while, but you still need to know the vintage to know what you're buying.
Consider my Cleveland Tour Actions (TA1s). I've held several sets in my hands and they each look and feel different. Not drastically different, but there are some subtle changes here and there. The difference with TM and Callaway irons is that from one version to the next they might lose die hard fans of that model. Hopefully TM gets some people back with their 2011 lines, because they're rather compelling, but Callaway? Not sure what they're after this year (very gaudy - sort of like Nike a couple years ago).
I think the main difference in all the clubs is mainly new product launches with several different modification. For example the biggest difference between the Diablo Edge and the Diablo Octane is that Callaway used their new Forged Composite material in the clubhead. I'm guessing they used names similarly related because their similar clubs but with some distinct differences.