As mentioned in comments on my original mild objection, I’ve been convinced that threaded discussions, new in the upcoming WordPress version 2.7, are a good value at the price. So today I slapped support for the feature into Simplish. This version of the theme should be considered “beta” quality, just like the new WordPress features on which it’s built. Both are subject to change before final release.
The demo shows a “jacob’s ladder” style for the comments/replies layout, where both left and right margins are indented per-thread-level. It’s an (experimental) attempt to ease the “comment chaos” feeling a deeply-threaded discussion can give.