I did use ToWx5 a lot -- but I don't find using my characters' abilities (I spent talent points for) an "abuse". Analogously, one could argue that using 3 sheeps in a group with 3 mages is "abusing" a "stacking" CC -- here too, all party members benefit from the "stacking" effect. But this is not the type of discussion I would like to have here. I simply don't like being accused of abusing something that is perfectly within the game mechanics and well-known to the devs.
ToW appealed to me because it served two important purposes in PvE: Firstly, it got my characters spell-hit-capped in PvP gear, and secondly, 51% crit total helped save mana and thus compensate for the lack of mp5 on PvP gear.

In my opinion, ToW stacking was removed, because:
a) most major buffs were made raid-wide, and
b) stacking ToW (as well as many others) would have been OP

I do not think it is likely that Blizz changed the buff system because of a few multiboxers.
It's more of a necessity that came along with all the other changes to classes and the raid- and buff system altogether.

Sad thing is, Blizzard's efforts to balance dps classes seems to be restricted to:
a) level 80 (atm) and
b) raids (where CoE etc. is assumed to be up).