This has already been discussed in Language - 'wcf.clipboard' category
Alexander Ebert explained better than me the reason in the past:
(...)
At this point I'm thinking about dropping the ({$count}) thing completely with the next major, because these numbers are largely useless. It may give some additional information if only a handful of items are selected, but are completely void for more than that because it doesn't offer any additional information.
Just imagine marking 8 threads across the forums and when opening the dropdown, some actions will report less numbers. Not only is this confusing, but is also completely useless because it does not reveal which items are affected or not affected.
Totally agree, currently this method is confused and useless.