This is the truth of it OP. You are 100% wrong. You wife is far far FAR better than you think, comparing her with the average gamer. As bad as your wife is compared to real hardcore gamers, you must understand that hardcore gamers are in the extreme minority. Your wife is probably in the top 10% of all gamers concerning skill level, because the sad truth is that most people are bad.
Look at it this way. Wow has 11-12 million players. Most of them are not level 85. Of those that are 85, most have never set foot inside of a raid, let alone downed the first boss. Most raiders are going to be somewhere in between your wife's skill level, (good) and the skill level of those that have yet to reach 85, (so bad it's not even funny.)
36890 Guilds in the world have killed normal mode Shannox. 33130 Of those are 10 man guilds. 4265 Are 25 man guilds. Assuming each 10 man has 2 backups that have seen the fight, and each 25 man has 5 backups, that gives us 397560 people that have killed the first boss in 10 man, and 127950 people that have killed the first boss in 25 man. That gives us a total of 525510 people that raid. Just around 5% of wow's playerbase.
Even if we assume that only half of the normal Shannox kills are reported to wow progress, that leaves us with about 10% of the playerbase having killed a raid boss. This is with the Firelands nerfs, and that number starts to drop off substantially with each boss. If your wife killed multiple normal mode bosses before the nerfs, I think that puts your wife firmly in the elite raider category compared to the majority of the playerbase.
Also, your example of FPS games isn't a very good one. Games that are mainly pvp focused have a much smaller playerbase than wow. For example, I could get on Gears of War 3 right now, I doubt there will be more than 40k people playing Team Deathmatch, the most popular gametype. Most of the people that play games like that for the pvp, will have a much higher skill level in general.
Also, your car analogy is spot on, but your conclusion is wrong. In other words, I shudder to think of how many people were killed by drunk or incompetent drivers in the time it took me to make this post.
I don't think wow is the bottom of the barrel concerning skill level though. Wii Sports probably just barely beats it. Barely. And that's exactly the sort of people that make up Blizzard's primary demographic.