OK; again with the 'amateur' mistake, however, on the substantive point, yes, you're better off with FOSS. Don't forget that the basis of your entire argument is that you're prepared to pay for support. In that case when the original programmer drops the code, and if no-one else volunteers to pick it up, and you can't program, then you find someone who can program pay them to pick it up. With proprietary code, once it's gone, it's gone. It doesn't matter how much money you've got to throw at the problem, you're still locked out.

Also, in case you'd somehow not noticed, most of the N900's operating system is free software, built by paid professionals, including those working directly for Nokia. With FOSS they've had the advantage of building on an existing system rather than having to start from scratch - how, exactly, would any of us be better off if they'd tried to write their own proprietary OS from the ground up?