First off - I think it's a common misconception that higher mash temp = sweeter beer. It adds body, not sweetness.
John Palmer disagrees with you: http://www.howtobrew.com/section4/chapter20-1.html
All things being equal, a higher mash temp will result in a higher terminal gravity...sweeter beer.
I dunno if you read that page or not... he differentiates between caramels and dextrins. Dextrins are a result of mash temperature, and he states:
Dextrins are tasteless carbohydrates that hang around, adding some weight and viscosity to the beer.
Caramels are a result of the grain bill (and to some degree, any boiling involved), and he states:
These sugars are only partially fermentable and contribute both a residual sweetness and higher FG to the finished beer.
It is true that you might obtain a higher proportion of maltotriose with a higher mash temperature, and in combination with a yeast less able to metabolise this - you'd get a sweeter beer. Something like S-05 however would just chow down on that too. The remaining beer in such a case would have higher body (more dextrins), but no additional sweetness.
