Capacity appeal
I don't think that most Americans actually know which capacity they need.
So they go with the bigger the better.
And quite honestly, I can't fault them. While 3.x cuft is adaquate for most normal sized households, if I could get a 4.x cuft machine for less money, the extra capacity would be nice.
Keep in mind that with modern machines and longer cycle times, running less full loads is actually kind of appealing for generally shorter cycles.
And you can fill less in a bigger machine, but more in a smaller one might cause issues.
But yeah, the heater option would be a must have if they ever come back. I mean, it was there, and it really isn't the most expensive feature.
The programming already has it in place, so the relais will be there as well.