I never liked
StarCraft and I haven't played the sequel, so I can't answer there. However, I can probably shed some light on MMOs like WoW.
The main draw to MMOs is the social aspect. Sure, lots of games have multiplayer today, but gamer interaction is usually quite limited. MMOs, on the other hand, not only thrive on gamer interaction, but demand it in order to succeed.
This is why guilds or clans (or whatever names they're using now) are so popular. You get a dedicated group of friends to play alongside, which is something you rarely find in non-MMOs. MMOs are, in a sense, a "team sport."
When Maia and I were playing
Guild Wars, we did so almost every night. Our situation might've been different in the sense that it was our ONLY way of interacting (beyond instant messaging and talking on the phone) while I was in Houston and she was in Edmonton. If you don't know how far apart those two cities are, just
take a look here on Google Maps.
We've barely touched GW since we finally moved in together. That said, we're both very interested in
Guild Wars 2. We don't know if we'll necessarily buy it, but it's definitely a game that has some potential for us.
You'll also find that there are relatively few players who do nothing but "play all day and night long." You'll hear about the extreme cases since those are newsworthy.