Why do companies put up with the 1-3% share of the bank for an IPO? What is the service the banks provide, and do they have more work if the IPO is bigger? Othe

Why do companies put up with the 1-3% share of the bank for an IPO? What is the service the banks provide, and do they have more work if the IPO is bigger? Otherwise, why not give them a flat fee? I suppose Facebook could whip up a trading system for "virtual FB shares" on top of FB on a weekend, no need for banks and stock markets at all? Some lawyers to comply with regulations, though :-/ They already have their own currency, so presumably also an infrastructure for transactions and so on.