This is the big thing with these arguments. Smart people
know each OS has its pros and cons. There is no OS in the world
ever that suits everyone.
Hardware-wise, it isn't really that big of a deal. Think about it, you don't buy a Mac to play games so you don't need massive horsepower. Yes, there is stuff like media creation and manipulation which requires grunt - and that is when you buy a more powerful apple workstation designed for the task. If the software you need runs in Windows, by all means run Windows. As said, many people prefer OSX-only software, or just prefer OSX versions of software. I know a bunch of guys who use Adobe suites on OSX and they think it runs better than in Windows. Could be entirely subjective, but if they work better on a Mac then why shouldn't they?
The world is full of things that you pay a premium for. I was stood outside a watch shop in Manchester today drooling over a 10 grand Breitling. People pay this kind of money, and more, for watches every day. Yet if you get right down to it, it does exactly the same thing as a £100 watch from Argos. The difference is the quality, care, attention and support.
An Aston Martin DB9 and a Vauxhall Astra do the same basic thing. One is massively more expensive than the other. Again, it comes down to quality, attention to detail and so on.
At the end of the day if
you want a Mac then go buy a Mac. You should not have to justify to anyone what you do with your own money. Smart, knowledgeable people will understand you have chosen a Mac as your preference and will not question it [unless you made a schoolboy error and bought one to play games on!

]. The person who
does question it will be the Windows fanboy and nothing you will say will ever change their mind.
Even with stuff that is very similar attracts fanatic fanboyism. Take ATI vs nVidia. Some people are insane and insists their choice is the best, when in reality outside of benchmarks there is no real-world difference at all. If ATI vs nVidia can't be resolved, two completely different OS/computers have no chance.