Heh, "Decent" is more likely to make me apply than "Competitive" because it shows that they know what good developers cost and are acknowledging they're not paying top rate.
I don't think "decent" is any more meaningful than "competitive". Based on my experience, "competitive" has proven to be sometimes way below market value, I don't see why "decent" would be any different.
Some companies have no clue what "competitive"/"decent" really is, some do but are just trying to find someone to milk for cheap.
'Decent' could have a connotation of 'good' (though that depends on the source, and the location targeted) - it's in my vernacular, but would agree, it can certainly be offputting, and a case of your second point - milking for cheap.
How might companies tackle the issues some have listed here of displaying salaries, while not deterring people (assuming they're being fair, not exploitative).
Some companies have no clue what "competitive"/"decent" really is, some do but are just trying to find someone to milk for cheap.