It's not so much that someone will say "you should've used Oracle". It's that when your application is down for two days they'll say "you should've picked a vendor with 24 hour support and good penetration in the job market".
Now, your Oracle-hosted application might go down for two days as well, but then people would shrug and say "sometimes this happens."
To be fair to Oracle, though, it does seem to happen less often.
With our Postgres move, we worried slightly about Postgres support for the trickier bits, but (b) our Oracle support does Postgres as a sideline (a) there are less of them when you can do a PG cluster per app, and nothing actually has to play nice with anything else.
Now, your Oracle-hosted application might go down for two days as well, but then people would shrug and say "sometimes this happens."
To be fair to Oracle, though, it does seem to happen less often.