I think its mostly the cost and folk dont know the real treasures they offer. I'm going to get one in a few years. Linux is really good though and offers all the security one needs really. Windows gets allot of negative press with it having holes and stuff BUT remember its the most used OS and as a result it is criticize, attacked, probed and exploited on a daily hourly basis which is why the bugs are well known ... its kinda like this analogy with encryption as follows.
AES is the standard used and is widely linked with the US even though designed by Belgium's. When the competition was done to find a winner for the standard another well known cipher was used - Blowfish - it didn't win but has a wide fan base and really good ... I use it, very secure but like the security experts say AES is used daily, 24/7 by many corporations and government agencies the world over and so is probed, scanned and looked at often for hole and as of yet NONE FOUND as its never been cracked period. Compare that with Blowfish albeit very secure and probed nevertheless, its not on the same 'stage' as AES with it being the standard, so not up to the same scrutiny ... that gives a shadow cast over it compared to AES and how that has survived all these years, so the question could be would Blowfish have survived that same level of scrutiny? its not cracked either but its not had the same amount of probes on it like AES.
Windows is still standing strong with over 75% of the world using that as the OS. Its great for desktop but nothing wrong with a change.
Mike I will let you know that Military Intelligence in the UK use only ONLY Apple computers, laptops and other technology because its so secure.