Don't call 'em 'steelies,' please.
Anyway, for those rocking modern stem/handlebar setups on old threaded forks, then yes, a quill adapter is used. Not really any other way of going about it. I've never seen a stem clamp directly onto the steerer of a threaded fork – none of the steel bikes I've owned (five and counting) have had the steerer extend beyond the headset. If you saw a setup such as a threadless stem on a threaded fork without an adapter, then you've seen something that's probably not worth replicating.
The quill adapters seem to work fine. I've never had a problem with using them, even on older steel bikes that are my backup race bikes, but I keep things good 'n' tight.