I'll relate this to your scooter for you.
Yes you can go out and by an envy complete and ride that around all you want. Sure it may not have quite the deck length or bar height you set out for, but it does the job and comes in a relatively ready out-of-the box format.
OR
You can do a bit of research, try your buddies scooter and pick out some parts that really suit what you want. The beauty of this is that once you get all these parts, your going to spend an afternoon (maybe even a little more time if you want to be a perfectionist about it) and assemble it the way you want it.
This accomplishes two things. Primarily it "dials" out your scooter the way YOU want it, which makes the most sense seeing as each rider will have unique demands. And second, it intimately introduces you to your scooter, part by part, so that when you bend your first deck or strip your first SCS bolt you know why it happened and how to fix it YOURSELF. You're not going to go out and waste money and time on having someone fix something you use everyday for you because you know how it works yourself, and so you should: you built it.
Now the real deal breaker about your mac (The envy complete) is that every part and software aspect is controlled by the manufacturer. If this allegory between the envy and the mac were to be complete, the envy complete would have to come with every part locked in: bars welded into compression, axles threadlocked with permanent threadlocker and so on and so forth. Thankfully it doesn't, but a mac does.
I'm not saying you have to start by building your own PC because that can be a daunting task, but stay away from apple. They've falsely earned the name of being the "creative" choice as far as computers go, but in actuality most artists who know they're way around a computer will tell you they're a big waste of money.
After learning your way around a PC you'll find macs pretty much insult your intelligence.