htop-1.0.2 is compiled with --enable-taskstats in Gentoo. This requires CONFIG_TASKSTATS, CONFIG_TASK_XACCT and CONFIG_TASK_IO_ACCOUNTING in order to function fully. These are not exactly common options to have in a kernel, I believe. The ebuild should make the usual check for them.
In fact, the only option that matters is CONFIG_TASK_IO_ACCOUNTING. The others are necessary for this one to be available, but that's not interesting from the point of view of the ebuild, I guess.