https://bitcoin.org/en/release/v0.8.0
The info from the wiki is from 2011, so it might have been an unintended feature.
To be extra sure I just did some tests. I don't have the 0.8.6.1 bitcoin-qt any more. I tested with my ltc wallet which is v0.8.6.1. I edited the config file so that the datadir is pointed to a non-existing directory. I started the wallet with -conf=... and sure, it asked me if I wanted to rebuild the blockchain. I quit the wallet and changed the datadir back to the correct directory in the config file. The wallet can start normallly. It proves that at least v0.8.6.1 bitcoin-qt uses the config file to define datadir.
I suggested this is a bug in the technical forum. My post got deleted