I think a lot of forums use it as an "anti" mechanism for people who wish to get "Kudos" quickly for every post they make.
Whilst the "Thanks" received for my good posts are welcomed they are not essential.
But I think the restriction on the number you can do in one session is a bit mean :-O:)):x
At the end of the day It must be forum policy and we must accept this.
Personally I now read all of the new posts since my last login and then decide who I am going to give "Thanks" to.
So it can work in a good way as you are being selective about who you are going to give "Thanks" to as it has been thought out from the previous sessions postings.