After reading other comments from around the web I think the real problem was that Nokia have been caught out with the enthusiastic welcome the N900 has been getting. They were expecting the N97 Mini and the 2 new music phones to be the devices of the show because they were announced at the show whereas the N900 was announced the week before.
I think they thought that the N900 would be a slightly more popular version of the N800/N810 but still a niche device. So they did not put much effort into keeping the network providers happy. Now its getting rave reviews they may be regretting that.
However I hope they keep the open nature of the N900 and keep any network provider interference of the device to a minimum. I think the open nature gives it a good distinction from Symbian and keeps both platforms viable.

There is always a chance that the network providers will take up the device if it proves popular and they get enough requests for it. If one takes it on and it does well the others will have to follow or risk losing custom. Yes I know they are big ifs!