I guess whilst they try to cater to those types of people, they don't want to portray the ones they are pitching their MacBook competitor to as brainless losers.
This exactly. There are basically two ways to use the "bad example" character in advertising:
Either the fan of your competitor's products is the annoying person that the target audience
doesn't want to be, or the person using the competitor's product
is the target audience and is being shown the right path. They're fundamentally different advertising targets--the former is insulting your competitor's users, the latter is trying to lure them.
The danger with the insult path is that you may end up insulting the exact people you want to be buying your product. You have to walk a particularly fine line poking fun at Mac users--there are lots of stereotypes you can try to make fun of them with, but because they basically
are the entire high-end of the market, unless you're selling commodity-priced junk you really
don't want to insult the majority of them.
Your best bet is to insult "annoying person who no one wants to be seen as" so you don't run the risk of alienating your target demographic.
This ad is definitely trying for that, by creating "annoying sorta-hipster Mac zealot you of course do not want to be", which might work because it's a recognizable caricature dating
way back, but because of the relative mainstreaming of Apple products is becoming a harder and harder sell.