I'm aware, I was already years deep into Django when they released it. But since it doesn't expose GROUP BY (the aggregation API only covers a subset of the uses), when you need it you have to drop to raw SQL, in which case your query will not return a QuerySet anymore, breaking compatibility with the rest of the codebase, defeating the point of an ORM in the first place. An uphill battle.
The GROUP BY still isn't exposed directly, but neither are joins or subqueries. The rules that make up what should be included in the group by are fairly elaborate. However, writing custom expressions will now allow you to craft some pretty cool SQL, and allow the sub-expression to specify whether it should contribute to GROUP BY or not.
Disclaimer: I did a lot of the work for query expressions in 1.8. The ORM team is expanding, and people are actively working on bringing more powerful features to the ORM.