2) Unless you're going into a graphic design/architecture type field, your Mac runs a high risk of not being compatible.
3) There are viruses that affect Macs and PCs and if you're smart, you'll have anti virus software either way.
2. Most people only need web browsing and some other basic software these days, and the amount of mac software has increased as they've gained market share in the past few years. I have numerous ways (VMWare Fusion, Wine, Bootcamp, remote into a Windows PC) to run Windows stuff on my mac, but I rarely have to any more. Last time I did was to use the scan tool software for my car, but most people don't need that.
3. If you're smart you don't need antivirus software on either. I don't use it on my PC any more, not even the free Microsoft Security Essentials. It was slowing it down too much. I'm careful about what I download and what sites I go to, and if I get bad luck I guess I'll just reinstall the OS. I don't mind taking the risk.
I wasted an hour on my work computer today updating it and waiting for it to reboot. My mac is no longer supported, so there are no more updates! But even when there were, they were generally quick to install. I don't use my PC at home as much as my mac, but every time I do it needs updates. There are other frustrating things, for example today Excel got lost on the invisible third monitor (I only have two monitors). I quit and opened a new spreadsheet several times, but eventually I had to change the screen resolution to bring it back. I can't think of a time when I've had a similar problem on my mac. My work PC gets sluggish after a while from having too many things open. I think the Aero interface gets clogged up somewhere, and I end up having to reboot. I can often go months on my mac without rebooting, though after a while it does help clean up after programs that leak memory. The weekly required virus scans slow down my work PC significantly, and they will never find anything. Over a year these things add up to measurable time, and unmeasurable frustration.
I've used Windows and Mac extensively, but I can work more efficiently on macs.
Macs are high-end hardware sold at a premium, with a premium OS. PCs are available on a wide range of hardware, and sometimes the low-end models give them a bad name. The OS is OK, but not the best. Instead of refining Windows 7 and improving it, they add unnecessary junk in Windows 8. I guess Apple is doing that too, but I've skipped everything after 10.6.8 just like I've skipped everything after Windows 7. Maybe Windows 10 will be better.
An example of a frustrating feature of Windows 7 is the control panel. I grew up with Windows 98 through Windows XP, and the windows XP control panel buttons are burned in my memory. Add/remove programs, Printers and Faxes, and Device Manager are some of the common ones. In Windows 7 there's Device Manager and Devices and Printers. The difference is not clear, and there's too much stuff going on in the icons for them to be useful. Plus, if I try to use the search bar to get to one of them quickly, I have to type "Devices..." or "Device M..." to get the right one. On a Mac, the first three letters of all the system control boxes are unique, and in fact the first two letters of all the built-in ones are unique, at least on mine. And, while the icons are not the most useful, most of them have different visual content, so it's easy remember the one you want and find it at a glance. The Windows ones are all round glassy silver with a lot of stuff going on. Why do Folder Options and Default Location have check boxes in the icon, and Administrative Tools has two!? None of the other ones have it, even though these are all options. Date and Time, Recovery, and Regional and Language options all have clocks, and they are all set to three o'clock. Why? On a mac, Date & Time and Time Machine both have clocks, but the Time Machine icon is much different (and set for four or five o'clock). On a mac you can type approximately what you want on the system control window search bar, and it highlights relevant buttons. With Windows you have to know exactly what it's called. For example, on a mac you can type power and it highlights Energy Saver. It's little details like that which make a mac less frustrating to use for me.
Edit: Forgot to add that the icons in the Windows control panel may be in a different place depending on the size of the window. The only way to get an alphabetical list is to make the window tall and really narrow. The mac system control doesn't let you resize it, so they are always in the same place.