However, LL also came with completed spell lists and monsters, which meant I could plug in the changes I wanted to test without having to practically build a game from scratch anyway, so it won.
Microlite20 has monster lists and spell lists, they just get there own (usually) 2 page rules sets instead of being in the core rules. However, they aren't nearly as complete as those in LL or BFRPG. The current versions of microlite20 are designed for folks who already know how to play (and probably have access to the D20 spells and monsters).
I'd love to see a set of complete rules for M20 designed for new players who have never seen a set of RPG rules. I suspect quite a bit of game could be packed into 16 to 24 pages with reasonable "how-to" descriptions, examples, spell and treasure lists, and monsters. The short rules could be included as a summary sheet.