So, say you need Xcode installed (or updated) because you need GCC and/or other development support tools on your OS X 10.7 machine. So, you launch App Store expecting to install (or update) Xcode easily enough but are met with one of two messages telling you that you’re SOL.
At this point it seems like you’re forced into paying to upgrade OS X but there’s an alternative. Albeit, not an obvious one. You can download older version of Xcode if you have or create an Apple developer account. The direct link to the Xcode downloads page is: https://developer.apple.com/downloads/index.action?q=xcode
Note: If you’re running OS X 10.7 you’ll need (as of this writing) to install Xcode 4.6.3 as Xcode 5 requires OS X 10.8.
It just works, right?