Here we go again....
The difference in overall perceived picture quality between interlaced and progressive DVD is frequently as much or more dependent on the TV's calibration (both user and service level) as on the relative merits of deinterlacing in the two machines.
Many 480p-input-capable TVs have separate service level settings for 480i and 480p input scan rates. And most still run BOTH rates through the TV's scaler.
Unless you have had the set professionally calibrated for most accurate picture at both scan rates, you simply cannot assume that what you're seeing is entirely (or even primarily) a difference in deinterlacing quality. It could be explained by presence or absence of many other settings or problems such as sharpness, edge enhancement/SVM/ringing, bypass of various processing (e.g., bypass of aspect ratio control or PIP with 480p input only), etc.
Now certainly, if the TV's scaler lacks inverse telecine (film mode deinterlacing), the 480p DVD should look better in that one parameter, but that is just one parameter.
So I always advice caution on these types of comments, especially when advising someone on a purchase decision. The configuration that one person clearly sees as "better", may not be the best possible with the equipment at hand.