Nope. Xcode 3 was free, and XCode 4 cost $5 or $10, can't remember. REgistered developers got Xcode 4 for free though.
XCode 4 only costed for SL because it was the default platform for Lion, not for SL, but Apple offers it for SL users for 5$. But in any case, as long as you are developing for the OS you are using, you get Xcode for free.
Please stop spreading BS... Xcode 4 is the latest version of the IDE, it doesn't matter what you develop for, if it's OS X, iOS, etc. You DO NOT (or did not whatever) get it free for the "OS you are using". I wanted to develop for SL, and xcode 4 was still $4.99 a few days ago. The only thing free was the OLDER 3 version.