For us the combination of WoW and WC3, then later LoL, are what ruined the thriving LAN centre scene across Ireland. There were 12 or so actual GAMETHEWORLD centres, then other wee franchised ones. WoW especially just didn't lend itself to LAN gaming, absolutely sucked the life out of the centres.
The issue that was noted at larger LANs I used to go to was that matches of DotA could lock in around 12 people for around 45m per game which would make getting participants for other games more difficult. There would be constantly running CS/UT servers where people would drop into to kill time, but trying to get a large game running or something like battlefield required advance planning
