How about a (literally) one click installation to Heroku?
That covers the convenience factor well, but not the cost factor. Heroku's great for the right kind of app, but no-one would have heard of WordPress if it required a Heroku install.
Aaand now you're back to the "platform dependent on a single company" problem.
Fair point.
as mentioned before they could follow the Wordpress model with one-click install for individuals that one a hosted solution.
And a download option for those who have the expertise to setup their own server.
What if you could one-click deploy to Heroku, OpenShift or AppFog? OpenShift can even have multiple competing hosting providers or you can use the free hosting from Redhat (which includes a LOT more resources than Heroku's free plan). And of course you could still do the traditional dedicated/VPS type installation.
The problem is that I'll want one-click on something that you didn't think to support. For example, I want to put it on Windows Azure :)
I wasn't that familiar with Azure, but I had heard that they had Linux VMs now (which would be one option), but I did a little digging and it appears you can actually run RoR apps on the Windows side as well: