Travel to site provided/reimbursed

The travel companies I have worked with have always provided travel to and from the site, as well as a rental car if the site was (+ or -) >5 hour drive from home (above and beyond the compensation, per diem, housing, benefits, ect..).  But I have noticed that other companies contacting me lately do not, or are no longer providing this.  Sometimes only as a reimbursment for travel to and from the site.

Is this just greed on the side of the travel company, to push these costs onto the traveler?  Or do the companies actually reduce the amount they charge the sites for "providing" the traveler? 

I have been offered this as an option, not as a rule on any contract thus far.

Wow!  Stay with those companies.  Although, every company is about making money.  And as healthcare costs/coverage changes, plan on what they offer to change. 
There is a number for every assignment & all money comes out of that number.  You would probably make more each week without the car.  Some companies just know how to better "move" money around in that number.