Because the copy is finished before WOW TBC Gold release, yes. Classic contains all the characters, therefore there is no delay for copying when you choose Classic. If you choose TBC the copy may cause downtime (just because its not instant) and imagine a lot of people's characters being copied at the same time which could slow the system down.
Bots are likely to take advantage of the boost, making it even more challenging for bots. If bots were managed, the boost wouldn't be cheap Burning Crusade Classic Gold a problem. I have 5 friends coming to classic, as we all love tbc and only due to the fact that they can increase their levels beyond the vanilla levelling content.