Even if you're very flush it's handy to have the ability to use a credit card for a transaction because your checkbook is at home. Maybe you want to buy something and then sell some stock when you get home to pay for it? Credit is handy when you don't need it. I would imagine :)
Speaking only for myself, my total credit limits are huge because my wife likes signing up for new cards to take advantage of special offers and rewards programs. We don't use anything like that much credit, but it's available to us.
Sure but you don't have any obligation to keep the cards and pay fees year after year. When the annual fee is coming up on a card I call up and cancel it. Most cards give you the first year free anyways. Plus the no annual fee cards add up if you've been "collecting" them for a while and there's not usually a reason to cancel no annual fee cards.
Total it would be like $300, but all of them are "first year free".
Plus usually you can call and get the second year free too.
Regardless, I can cancel w.e. and the increase in my credit score is worth it. At the moment if I want to buy a house (for example) I get the best rates on loans
Many cards are first year free but quite a few aren't. AMEX stopped first year free on a lot of their cards. Regardless if I'm getting a bonus I'm subtracting any fees from that bonus to see if it makes sense. If a card is $100 annual fee and the worth of the first year is $500 it's a no brainier to get $400.