So knowing that, is there any good reason really to by a "for mac" USB drive really then like a Western Digital USB one "for mac" if you might as well buy one for PC and format it for Mac?
exactly!
Also, can you format a USB NTFS drive on Mac OS X to a different format so you can read/write?
Yes you can using Disk Utility. Your choices are:
. HFS+
. FAT
. exFAT
FAT and exFAT file systems will work on most PC computers (read/write). But you have to understand the limitations of each of these file systems:
. FAT32 will work with volume up to 2TB and a file size limited to 4GB
. exFAT limitation is in its file directory. It does not have as many security in place for recovering files in case of a disconnecting media during read/write operation for example.