[CentOS] mdadm RAID sync speed limitation?

While creating some arrays this evening, I noticed this line my dmesg:

md: using maximum available idle IO bandwidth (but not more than 200000 KB/sec) for reconstruction.

Why is there a 200MBps limitation on the mdadm sync speed? It certainly isn't a concern for my particular systems (15k U320 SCSI) but I can imagine there are much higher end systems that actually could sync at a rate equal to or higher than the limit. Is this limit arbitrary? Based on detected system specs? Limitation of mdadm itself?

Just curious.

--Tim