Apple puts together a very pretty package and basically dictates what you will run, how you will run it, what you can do with it, and where you can do it.
You can run anything you like on any Macbook. And as other responders have noted it DOES solve the "too many models" problem, there is a limited selection of base models. It's basically, do you want an air or not and how much memory (RAM and storage) with reasonable defaults so you cannot go wrong simply ordering default configurations.
You will still have software problems.
Here's the key thing. Yes, you will have software problems. But who will solve them? If you are helping a friend buy a PC it's YOU who are solving them, that's who.
If you help someone buy a Mac you can simply say "try the Apple store Genius Bar first". Chances are they can help, they generally are pretty competent and pretty technical.
You still have viruses.
Actually no. There's one virus, one, that was from a Java installation, and an OS update already closed the hole. And you would have had to go through a chain of trouble to activate it... not a virus at all in fact.
But even ignoring the technical definition the truth is that unlike a PC, generally you can let a non-technical user go for years with a Mac and be pretty sure they will not have a virus.
You still have software problems with upgrades.
Actually that is REALLY rare, and again - Apple Store, not you. I have not had upgrade problems in years with any Mac software updates.
People still need to search some forum from time-to-time to figure out how to fix some strange new issue.
Or have someone help them for free, at an Apple Store. Are you starting to get what makes a Mac such a great idea for non-technical users? How is a non-technical person supposed to search forums for "odd problems" anyway? They cannot.
Ever try and build something from Ports only to have it *not* friggin work when you upgrade?
Come on man, that's not something the original poster is going to find a problem. If you are compiling UNIX utilities yes you may have some hiccups, but even then you can usually just recompile!
Apple has gone to great lengths to make the use experienced top-notch, but it still has it's problems just like Windows
That is the biggest misconception. I still have to help people with modern (Windows 7) pc's from time to time. Macs do NOT have problems anywhere close to what non-technical windows users have every day.
To even think about buying a non-technical user a Windows box and all the inherent baggage that comes with it is simply cruel to my mind - and it's a cruelty that as I said will be punishing you as well as the recipient.