Do most manu. buy or build their x-overs?

There is quite a bit of discussion concerning speaker driver manufacturers (scanspeak, vifa, morel, etc.) and who uses what. But in general I would say that drivers account for less than half of the overall performance of the speaker. The crossover is a HUGE factor, in many cases perhaps more important than the drivers themselves.
So, generally, do most manufacturers of high end speakers purchase their crossovers in the same manner? Or do they build them to suit the selected drivers?
If they are purchasing them, who are the big names? While I can name off a dozen driver manu. I can't think of one x-over manu., only a few designs named for their inventors (presumably).