Is it called for? Well, sort of. You see this has really pissed many people off, and there are loud murmurings of MOS-based developers doing the same with their software - allowing everyone to use their stuff for free, and charging OS4 users. If there was a way to divide the community further, stunts like this are great. Jens isn't supporting MOS because it's impractical, he's doing it out of pretty obvious spite - he could support multiple platforms just by using OpenPCI! I'm sorry I ever bought my CW3 from him now.
And he's talked himself out of better support for the CW4 SIDs from the MOS side - if you remember itix was the first to support CW3 for Frodo, and left the open source for anyone else to do the same. Needless to say he can't do this again for CW4 if its 'not designed for' the machine he uses.