Purely empirical of course, but evidence none the less.
About six months ago the company that I used to work for took a turn for the worse management wise. Without going into too much boring detail, they basically decided that due to the current economy (I was in Michigan working for a auto parts supplier), they could do whatever they wanted to their employees, including laying them off for a week here and there, cutting pay and mandating ridiculous work hours.
When I started there last year, I was on a team of 5. Over the course of three months, every single team member left for greener pastures. That does not count the people on different teams that have left. While I would agree that on any single decision it is only a whining threat, when those decisions start to add up it points to a bigger issue and will eventually cause "top-flight" admins to seek employment elsewhere.
While neither a lover of Microsoft or Apple, calling Apple a monopoly is simply ludicrous. They hold about 3% of the global PC market (~7.7% in the US), 1% of the global cell phone market, and by some estimates about 23% of the Personal Digital Music Player market (Source: http://tinyurl.com/nm3m4n). Certainly not a monopoly in any of the markets. Microsoft on the other hand has ~90% global market share.
As far as why Apple is not abusing monopoly laws with their iTunes software as it relates to the iPod, for the same reason that Blackberry's and Palm's software does not abuse monopoly laws for connecting to their devices.