I am not an expert regarding this and have no experience working with very high traffic websites, however my first thought would be that the database newgrounds works in such a way that update operations are computationally expensive.
There's a lot of things you can do to optimise databases such as using different database engines, adding indexes and partitioning tables. However people mistake optimising for "making it better", this is rarely the case with current computer technology and is more a trade off of one thing for another.
Newgrounds' database is most likely optimised towards finding data very fast at the expense of making adding and updating information much slower.
Either that or the Newgrounds code monkeys don't know how to do UPDATE queries. ;)