It's quite different, might be hard to explain probably. (if i put many dots is to try to explain it in the best way i can.
Let's first see the two differences: the rates.
Let's try make it easy: for EXAMPLE
Following realm info Icecrown is a x7 exp, while Lordaeron x1, theoricallly this means Lordaeron player will be 7 times slower then Icecrown players.
On Icecrown it takes less then a week of casual playtime to reach level 80, thats why BG doesnt pop unless twink battles....Simply because in the time i que for BG, and see it pop, i might be already higher level or doing something more interesting.
Icecrow levellers do not que into BG cause they know that unless in a specific que / luck time , people on a x7 are more focused on get level 80 fast, to enjoy the max level experience, altho, Lordaeron plays interested in the pvp while levelling will be an add to the people in que from Icecrown. I GUESS, it might help out the overall ques, cause Icecrown players will know there could be a higher % to see the BG que pop. In any case lower brackets will always be dominated by twinks , i personally had a level 60 and a level 70 twink on Icecrown, levelled them up after the low activity.
I repeat, answering to your question, it's dead cause it takes a bunch of days to level 80. Having Lordaeron crossrealm might help out,cause the people will stay more @the level range , but quite sure wont help much. Whoever want play low level bg, will make a twink, the others simply dont care and want rush to level 80.