You're deluding yourself if you think you'd be as valuable to an early RoR-based company as a good dev with a year of Rails experience. I used RoR for my start-up because I was sick of PHP and wanted to learn Rails, and I feel immensely more productive now than I did when I began. And I'm a "quick learner", too.
Familiarity with Active Record, and making it reasonably performant, handling rails security issues, experience with the gem ecosystem, understanding the intricacies of the routing DSL, getting a handle on reasonable rspec/capybara or cucumber practices, ruby metaprogramming, knowing the Rails conventions and what it looks for automatically in controllers, views, and partials, and which methods are available where, knowing all the various helper methods rails provides for text processing, working with dates, and html tags, best practices integrating with AJAX, migrations, rack middleware, the asset pipeline, etc, etc. I've been working on our Rails app non-stop for 9 months now and every day I learn new stuff.
Long story short, for a start up which needs to iterate fast before it dies, acclimating a competent programmer to the "Rails Way of Life" just might not be worth it. Now, it's a completely different story if you have important domain specific knowledge, and the company is working on something especially innovative, but it seems like a lot of start-ups are scrambling for a pretty low-tech piece of the pie where "execution wins". My point is, Rails is surprisingly big, and while you can become useful in a matter of weeks, you can't become extremely productive with it for awhile longer.