A Twitter paradox

I have a question for Twitterati. I see a lot of people on Twitter begging for new followers. They want to get their follower count up to a magic, round number, such as 2000 or 4000. I wonder what do they do when new people follow them after they reach that number? Will it break the magic and the race will start all over again, from 2001 to 3000? But there are also a few practical questions:

1. Do those people follow every follower back? (Aside from spammers, of course.) Because it's not fair to beg people to follow you if you have no intent to reciprocate.

2. If so, when do they have time to read updates of 2000 people? I can barely keep up with the 100+ people I follow.

3. Maybe their secret is that they don't read the updates of everyone they follow? While the Twitter web interface doesn't let you group your followees into those you read and those you don't, there may be Twitter clients that let you create groups, filtering out the wheat from the chaff. I don't know because I don't use any clients. If that's what those people really do -- read only the VIP updates while ignoring the unwashed masses -- then it's doubly unfair. The ignored followers don't even know their updates aren't being read.

So I'm curious to know how this works. Not follow back, secretly ignore the bulk of followers, or make an honest effort to read everyone's updates and not get anything else done? I hope Teh Interwebs can enlighten me.