For example, you focus on Silicon Valley where you are extremely well connected. Competitors could do very well by simply focusing on less glamorous, but emerging startup hubs.
You require people to relocate to Silicon Valley for a few months. This shows commitment from both parties and is a smart choice for you, but it also makes the program inflexible and unsuitable for a great deal of talented, perhaps more experienced people who cannot easily relocate. Your typical candidate is a student who is fresh out of college. Your competitors may capture the value in other demographics which have less flexibility when it comes to relocation, ability to quit their job, and so on.
Imagine an Untyped Lambda which offers similar terms to yours, but is also very flexible. You don't have to relocate (you can work remotely). Oh, and you can also apply if you are going to do this part-time, if at the moment you are employed and want to see where the startup goes before quitting your job.
You may think that this idea is grounds for a complete disaster, that such candidates might not committed, and so on - but perhaps, just maybe, such a degree of flexibility would lead to all sorts of new talent giving entrepreneurship a honest shot.
I'm not advocating that you do all that, but rather that a smart competitor may use it to their advantage.
To be honest, that doesn't sound like a very promising investment opportunity.
YCombinator isn't a charity - they need things to succeed.
* Barriers to entry not commonly seen in the web/mobile space (complex bureaucracy + entrenched players with opposing interests able to grease that bureaucracy, etc.).
* Lots of disparate stakeholders that all have to be coordinated and managed (healthcare: govt, taxpayers, patients, doctors/staff, insurance companies. Education: Parents & taxpayers, teachers unions, students, local+state+federal govt.)
* The market is not traditionally tech-savy and/or early-adopting. Users have to be actively convinced. Getting traction is even more of an uphill battle.
* Anywhere the risks to loss of investment are not transparent or clearly understood.
Maybe all markets are like this to an extent, but some moreso than others?
government regulation
If Larry and Sergey had done their post-graduate work in Moldova, the world wouldn't have Google. (Remember they shopped Page Rank to places like Yahoo, who didn't want it. As an idea, no one believed in it.) The connections at Stanford gave them access to capital which they otherwise would not have had, which allowed them to prove the concept. Without that funding, Page Rank would be just another dissertation.