Absolutely not true. JBoss is a true open source project that doesn't require any sort of purchase... nor should you feel obligated to make a purchase. That said, the freely available documentation is not very good so if you are going to use JBoss seriously then you should consider purchasing the paid documentation. Truthfully, even the pay-per-view docs are not really that good. My suggestion is to be prepared for some frustration when learning JBoss.
As for your last point, any part of JBoss can be openly discussed. The trick is finding someone that knows. Now where did Norman Richards go when you need him...
It doesn't appear that a version without Tomcat is offered for the 3.2.X branch. Though to be honest, Tomcat does not add much to the size of the download... probably only 5 or 6 MB and compared to 45 MB that isn't going to affect the download size much. You could choose to download the source code and build it yourself. Even if you did this you would then need to manually integrate JBoss with Tomcat and that is going to be painful for a JBoss newbie.
My suggestion: Bite the bullet and download the whole thing.