That isn't quite true. A lot of recruiters that I've met get paid based on the salary of the recruited, so fewer people at higher salary might make the recruiter more money.
Simplistic EG (and a 2x 80,000 vs 120,000 is realistic), but, like a real estate agent, the cost of NOT closing the sale is greater then pushing for a marginal increase in the sale.
EG salary, pushing for 115,000 vs 105,000 the difference in fee on 20% is 2,000. Which is ~200-400 dollars difference in commission. Losing the offer for pushing for 115,000? 2,300~4,600 (10-20% of fee).
Your making some interesting assumptions like it is three times as easy to fill a $65k spot than a $120k spot. The recruiters I knew had pretty good contacts that gave them the ability to place highly paid salaries (Oracle DBA, SAP developer) at a pretty good clip, much better than the generic recruiter. Their shooting for the higher-end gave them the right reputation to do this well.
