So many EU (and now NA1) maps are straight cav fests. All open ground with a few buildings in the middle. It makes perfect sense that ranged players want to be in the one spot on the map where they won't be lanced in the first minute of battle
edit: I'll also add that my point of view is from that of an arbalest player who has to stand there exposed and reload for 10 seconds between shots
Most archers don't even have problems dealing with cav on completly open ground. 1 cav vs 1 archer on open ground : archer wins because he either OSed the cavalry or OSed the horse then the guy. Even worse with throwers. Xbowers are either hybrid and can defend themselves, or so agi-oriented that they are impossible to catch as a cav.
So even without roofs ranged are a difficult target for cav. If the archer is not 100% unaware of you, you stand no chance and have to flee.
Fact is, my kills as a cav are probably 70% of infantry, 20% of other cav and 10% ranged.
Roofs make this even more one-sided by making the archers absolutely immune to both cav and infantry. What would archers think if suddenly all melee troops got an armor that negated all ranged damage ?
Well that's exactly what ladders are, but the other way around.