Hi!
Domas loves to hate.
I hate just chronic whiners, who start calling you idiot after you misspell their name or leave weeping after minor criticism, but to not limit criticism they emit themselves. I do not have issues with other people ;-)
To stay on topic - we might want eventually to put covering index for all contributions-based operations, but still, for this operation we may want to keep a separate table (and do that for most queries, that need aggregation). For different traversing methods covering indexes are way to go.
BR, Domas