Gamedev.stackexchange.com site is about developing games. Any sort of games.
We allow questions about all sorts of languages, about the creation of downloadable games, about PC games, about mobile games, about freely downloadable games and about commercial games. We have questions about DirectX, about OpenGL, about Unity, about GameMaker, about Flash, about XNA, about Construct, and dozens of other languages, tools, and platforms.
Why in the world would we want to limit participation in the site's events to just one small fraction of our users?
No -- our site events should be inclusive. Participating in a game jam isn't about winning -- it's about participating; about meeting people. Showing people what you can do and admiring what they can do. It's about being a part of a community.
We should be celebrating the people who make this site what it is. Not excluding people on the basis of who we think won't get many votes and therefore shouldn't be allowed to enter in the first place.
Consider this a vote for "don't splinter the community".