That's a totally different scenario. Let's say I work hard on RS, legitimately, scrap together 100M only to have my best friend buy 500M and say herp derp, I haz the divine and virtus. All it took was IRL cash. It's annoying, but it doesn't affect my game (besides the point I could still kill him). And questing/accounts - really? How does this affect anyone else, the people who buy them - it's more people to play with, and quests are fucking annoying. It's the botters who come a tad close to ruining the game (sup, trying to slay black demons - joke, 300 botters in d meds).
Now let's look at Aimbotting. I buy Call of Duty in this case, on Steam. I log onto a server. I'm dead in a second, I watch the killcam, a guy's gun is going apeshit, autoshotting everyone in the head a whole game, now this continues for another 7 or 8 servers/matches (depending on which CoD). What the fuck? What did I just spend £40 on? That directly ruins the fun for everyone.
TLDR - The RS black-market does not directly affect the game for its' players - unless you want to be pedantic and include introduction of the trade limit, falling/rising prices, annoying anti-bot updates etc. Call of Duty aimbots directly affect the game for all its' players, I can't fathom why you would pay for a game to do nothing but cheat on it.
I know N4no responded but in case you were going to think up a counter-argument for him I've expanded.