It attracts people from the Windows world with its perceived ease of use. My biggest gruntle is that it makes the newbies lazy and hides them from the true powers of a Unix. I think new Linux converts should be pointed to Slackware first. The not so newbies should help them as best as they can. Only if they don't like this Unix way they can be advised to look at Red Hat and other similar distributions.
Most distributions come in two flavours, an official and a GPL'ed or free release.
In most distributions there are no differences apart from a printed manual. Distributions like Red Hat and Caldera contain a few non free applications in the official release. Red Hat and some other companies also give you tech support for some time if you purchase the official release. Companies don't make a GPL release on CD directly. Almost all distributions publish their work in ftp sites, other vendors like Cheap Bytes and LSL download those distributions and burns them on CDs.