Hardware concerns are valid. But more importantly, SPEC jAppServer is not a database benchmark. It's a Java App Server benchmark with a database component. To be fair, you have to change only the database, not the app server, hardware, and everything else too. Not to say that the conclusion is wrong, but it's very weird to say anything about database performance in this circumstance.
In our tests, which are database-only and data-warehouse focused, PG seems to be 3x-5x slower than Oracle on the exact same box, as it does not do data compression and is not as CPU-efficient. Which is quite respectable given the price difference, but may be a big enough gap to keep people who have money to spend coming back to commercial databases.