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1) All other things being equal, a new tire will consume more fuel than a worn out one. More mass, particulatly more mass in the tread area = more fuel consumption.
2) There is a technology tradeoff for tread rubber compound between treadwear, traction, and fuel economy. In your case, you went from a 740/A/B to an 800/A/B. In some respects that indicates the wrong direction for fuel economy. Further, your new tires are marketed as having great wet traction - another indication that this is the wrong direction.
However, we are talking changing brands and there is going to be some difference btween the way different brands use UTQG ratings as marketing tools. I am under the impression that Michelin under rates its wear values compared to other brands - and that makes 3 hits in the wrong direction.
Overall, this is only somewhat surprising.
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