A few thoughts:
1) Property ownership is one of the central tenets of capitalism.
2) At work, I am involved in a special assignment. Throughout the initiative, I've caused a lot of friction with various groups because it was perceived that I was infringing on their "territory".
3) Myspace allows users to customise their profile however they want. And people do.
4) My two-year old niece is going though a stage where everything is "hers".
5) Capitalism works better than any other economic system; my firm is very successful as an organisation; Myspace is a run-away hit; my niece is a happy baby.
Notice a trend? The only difference between you and a toddler is that you don't say "mine" every time someone takes your toy. Want to get peoples' support or to buy your product? Then remember this: property and giving people a sense of ownership is how us humans work. We take comfort in what we can control.

I agree with you about the ownership part, however I don’t agree that people think like two year olds (although there is a LOT of shabby thinking around).
I’d argue that it’s really about frame of reference — it’s inevitable that people with significant experience in narrow fields tend to see deep and complicated issues that are not obvious to the rest of us. Combine this with work overload and limited time to invest in understanding something that’s new and often they don’t have the right context to make sense of what they are seeing.
Framing the correct reference can mean pulling back on the vision, investing in sponsors, seeking supporters etc. — all the things that you’re doing and are making the initiative a success. Most importantly is that your organisation is a success because of one fairly simple thing – it knows what it does well and sticks to it, to change that path means making it clear that the new change will improve what it does.
In my experience, innovation is hard work, which is why I think it rests (for the most part — some of us still keep at it) with the young and enthusiastic who have yet to become battle-weary!
What I’m really saying is don’t mis-understand the blockers — appreciate they’ve earned their own fair share of battle scars and realise that more good ideas fail than succeed. Once you’ve convinced them of the merits and hit the tipping point, you’ll be amazed at how fast things can move, but it’s a hard slog to get to that point.
I like your comment about the blockers – that’s wisdom I have only recently learned – and I am starting to see the power of it now.