I don't consider it as useless. It's just the matter of terminology (pack < 20, set >= 20
Maybe I am harsh but I've got about 35k files here which can be described as icons and it's hard to find groups with less than my estimated value. Well, being honest: there are packs with ex. 12 icons BUT they are delivered in so many different formats (ICO, GIF, BMP, PNG) and sizes that my rule hardly applies.
The only situation I can say it's not worth to be downloaded is to give only one size of images because you can't use it widely. Even if your system supports scaling down (with nice antialiasing), 256x256 resized to 16x16 (or even 32x32) gives mess and you can just forget about "style". For many operating systems official guidelines recommend to provide at least three sizes for icons (MacOS X - 16, 32, 512; WinXP - 16, 32, 48; Vista - 16, 32, 48, 256; Gnome -16, 24, 48, 96; KDE - 16, 32, 48).
In how many places you can use icons in good looking way if they offer one resolution only? Docks, perhaps file browsers (if you like BIG symbols) and ...?