It is just i did not make my point clear enough. With linux as well as windows if you want support (beyond forums like this), then you pay,

Meego is open source and the community will provide a distro for the n900. That much is certain. The only question is if Nokia will support this distro- meaning customer support and service centres need to be aware of any differences. Supporting two OS versions raises the support cost. This is the cost I am discussing.

Without support from Nokia if you run the new OS and your phone breaks, service wont touch it unless you reload the original OS. As I said, being open source, the code will be available to all who wish to find it. The question of cost relates to support. I hope what i said makes more sense given the extra explanation, Think Redhat vs Centos