The 430 as well as the 530 and 480 does provide DME information that, so long as the installation is IFR certified, can be used to replace a separate DME. The 430 just doesn't have as good a display as either the 530 or the 480.
Among the 480's other nice features is that during an approach is provides constant relative bearing (an arrow) and distance to the end of the runway in addition to the distance to the next waypoint.
So far as I know the only time that GPS derived distance can't be substituted for DME legally is when flying a DME arc that is part of the final approach segment. Not an arc to intercept the final approach course, but an arc that IS the final approach course. And so far as I know, there is only one approach in the US that is set up that way. If you are feeling cocky, go fly this one!
http://204.108.4.16/d-tpp/0913/05222VDTZ15.PDF
Jay