There's a big difference in referring users & referring users who actually make any money. Even if someone is raking in $10,000 a month from a CPA company (which most don't) 2% is still only going to make you $200.
I've found that most referrals often make little or no cash whatsoever.
The most success I've had from referrals was from 2nd tier Casino Webmaster Referrals (until the gambling laws were changed), Textlinkads, Auctionads & Adult Friend Finder.
I've referred about 10 people to MoreNiche & about 10 to Azoogle all of which have made jack shit