Sharding is not that complex
Stonebraker can say whatever he wants - it doesn't make it the truth. You can read the comments in the original GigaOM post to see what some smart people are saying about his claims (which are off, non technical, and just FUD).
(Disclosure - I work for a newSQL company called ScaleBase). Now if you want to shard you data - there are allot of companies that do that transparently, one of them is ScaleBase. It's possible to shard with relational databases, and it definitely let them scale. Moving to a new database is much crazier than sharding an existing one (unlike what Stonebraker said).