It just seems that way. There are others, like Lin-ITX. But the Lilli's are by far most popular for their size/cost with Xenarcs a close second but more expensive.
What I haven't really seen is anyone come up with a screen that is cheaper than the Lilliput but matches the quality. There are endless posts by people who find screens for $125 on Ebay but they almost universally turn out to be video, not VGA screens.
One piece of advice - the screen is what you look at every single day. Get a decent one.