HDMI connections do NOT pass on ANALOG CC data
As most of you by now know, although many standard (and Blu-Ray) dvds offer subtitles, most ALL of them offer more detailed Closed Captioning. But here's the problem with Closed Captioning on modern dvd players:
The traditional, "analog" CC encoding scheme was designed for older, ANALOG devices and connections. Thus, when you have a dvd player that's connected to your tv via the newer HDMI connection and you play a standard (non-Blu-Ray or HD) dvd on it, you will NOT be able to view the disk's closed captioning - REGARDLESS of what you set the dvd player's output resolution to. Period. (Blu-Ray and/or HD dvds use a newer CC design that HDMI *will* correctly display on your tv).
Some - *but not all* - dvd players *will* correctly pass on the CC data to your tv if they are connected via the "component" connectors even if you set your dvd player to "upconvert" to something higher than 480i; others will not.
ALL dvd players will pass on the CC data to your tv if connected via the old composite or S-video video connectors.
So you see, the problem is NOT with "upconversion" per se - it's with the HDMI connection, plain and simple.
Sad, but true... we can "thank" the designers of HDMI for this mess. It STINKS, and stinks BIG-TIME.