While IBS is easy to obtain, and a good weapon in its own right, that doesn’t mean you have to use it. If you are sword specced, you can keep using a sword.
IBS is 51, and while there are more polearms at 60+, at 60, there is the Blade of Misfortune, which is a really good 2h sword.
Currently I’m at 4 points in sword spec, giving me 4%...one more level and I’ll try at 5%...but so far, I’m not impressed by the low number of times it seems to proc. I was curious about the polearm/axe 5% crit also, but it seems many other seasoned warriors are preferring sword spec, so I’ll try it out a little longer.
I guess the other reason for sword spec might be that, with gear and such, you already can reach about 25-30% crit rate, so you aren’t in great need of another 5% from the polearm/axe spec.
Raaze brings up a good point that at lower levels, this 5% crit may be more important than at later levels.