First off, for the record, I don't like what these guys are doing. They most likely don't have the author's consent, not to mention the fact that they are selling XDK developped software. For which, M$ can sue their ass off.
That being said (and hopefully I won't get flamed for the following...). I think there's an argument in these guys favour. They are not charging for the tools themselves but rather for the packaging of the tools. They are selling a convenience. And there are those who will pay for such a convenience instead of packaging it themselves. This would have been cool by me if they got the author's consent.
Many have done so before them. Just take Linux for example. It is totally free. But RedHat (and many other companies) packages Linux and sells it. The same applies for DVD-X. It is a collection of freeware packaged together and sold the the unsuspected public. They are selling the packaging and the easy of installing and use. Not the software themselves.
Let me re-iterate, I do not think what these guys have done is legal (from the XDK point of view) but I think there's a precedent.