Twitter has limits, though they aren't as stringent. For starters, you're only allowed to follow up to 2,000 people until you reach 2,000 followers. After that, you can only follow ~300 more than are following you at all times. This is done to prevent massive amounts of spamming, though it still occurs.

My only beef with your "limit" is that it would prevent the well-connected people from truly reaching their entire network. If you feel like Twitter & Facebook are too spammy for you, then reduce your followers and friends, but this choice should be up to the individual.