I don't see Xcode 2 on Apple's site, and Xcode 2 came bundled with Tiger Install CDs and DVDs. They have every rights to remove Xcode 3 from their site today -- right now, even.
That means Xcode 4 might soon become the one and only option to develop apps for Mac OS X and iOS, or to simply learn to develop on those platforms.
Just because Apple removes it from their site doesn't mean they stopped supporting it.
In any case, you own a physical copy of it in your Snow Leopard install disc. So you can install it whenever you want. There are incremental updates, like 3.2.6, which you can download today, and save somewhere.
Obviously Apple is not obliged to host every single update they released in the last 10 years in their website. I'm a paid ADC member and I can't download Apple Tiger DVD at the moment for example since they removed that from ADC as well. That's irrelevant.
You need to understand something. XCode 4 will never be forced on anyone who only wants to develop for 10.6 and iOS 4. That's Xcode 3.2.
XCode 4 will be only mandatory to develop for Lion, and possibly iOS 5.
And to develop for those platforms, you have to purchase Lion to begin with, which will most probably include XCode 4 anyway.
So you are practically whining for a problem that doesn't exist yet.