If I run
$ ulimit -t 5 $ yes
then yes gets killed after 5 seconds, but man and less/more don't.
Why are those two immune to ulimit?
My guess is that it's because you are limiting CPU time and these apps spend most of their time waiting on input so they don't use much CPU. Try more-ing a largish file and holding down space until ps shows you have used 5 seconds of CPU.