They don't, but to argue their side a bit: they'd say that the ability to exchange Starpoints for so many different airlines is essentially the same thing.

I look at both the Marriott Cheques and Starwood mileage conversions as a safety valve for someone sitting on millions of points and no possible way to use them all as award stays. Both of them involve about a 50% hit in value vs. a well-optimized award stay, but they both fill a need for some people. The last thing either chain wants is for an ultra-road-warrior to say "These points are now worthless to me."

Starwood also has those on-property awards...a few thousand points for a massage or whatnot.