I have CS3 Master Edition (got it for free from Adobe, after doing some work for them ages ago when it was the bee's knees in media creation) and it is a fantastic set of tools. There is very little genuine difference between 2 and 3 and even 6. The PDF creation tools and the pre-flight checks in InDesign are the same.
InDesign is just THE package for magazine layouts and other publishing tasks. The lighting and layering tools are great.
However Adobe has three problems -
1. Older CS2 licences are getting old and generate no revenue any more, but still cost money to support.
2. Great chunks of the SW market have become worthless, audio in particular.
3. SW sales are not doing very well and the future for large packages like CS6 is bleak indeed, hence the need to push cloud computing.
All the free copies of Windows that were flying around in the 80s and early 90s (e.g. bundled with Page Maker) is what made it the only commercially viable PC OS. Adobe are pushing cloud computing as hard as they can and getting people 'hooked' on CS2 will (they hope!) get them to take the small step of paying a modest amount each and every month for CS6.
In the past, you could 'borrow' a copy of Page Maker, Quark Xpress, MS Office, Windows, Corel Draw and many, many others, by just entering the serial number. This gives the SW manufacturer a large user base and takes market share away from competitors. Once this has happened, the manufacturer has to start tightening up security, bit by bit, until he can squeeze revenue out of all those 'illegal' users, who now need that SW and need the updates. In this case, Adobe wants them to sign up for the cloud.
Me, I'll stick with what I've got. There isn't much difference!