Could it be that the Exchange team thinks in "spreadsheets" and not sets?

I used a lot of "table" storage mechanisms over the years and could typically beat the pants off of generalized tools like SQL or Access. There were trade-offs. I got raw performance at the expense of things like ease of use. Coming from a procedural background I could see where they would want to make their light weight storage engine better and not have to re engineer the whole data laye t conform to SQL Server.

Then there is the whole licensing thing. If you let Exchange get away with embedding full SQL Server with no governors where does that put Express? I'll guess that a lot of big Exchange installs blow past Express limits without skipping a beat. The Exchange folks have got to be revolting against the "free" version having limits and then having to pay through the {insert favorite body part analogy here} when you cross a certain line in the sand.