I think I noticed the same thing, only my Dolby is not on (I don't want it on if I'm just using TV speakers, right?). I don't know if Sep 1 is when that changed, because that's when I got my 3400 (to replace the crappy Summit), but between the two it does seem like I have to turn the volume up higher. I think this is more noticeable on non-HD channels, as they seem to be quieter.
P.S. It's not a huuuge difference in volume. I'm used to having my TV on 18 (out of 100 I think), and now I turn it up to between 25 and 28 or so, so not super high.