It depends what you mean by "passes thru". If you mean "when its turned off, it passes the full HD signal from my cable to the TV tuner, so it can decode and display full HDTV", the answer is all recorders do this. But if you're asking "will the recorder tune HDTV signals itself and play them on my older HDTV that doesn't have a digital tuner" the answer is no, it will upscale as you suggest but the quality won't be near as good as direct tuning on a newer tuner-equipped TV or via an HD cable box.
Even if you have a new TV or recorder with QAM tuner for HD cable signals, it ain't a slam dunk. First of all, you need to have an HD signal on your cable, second, your TV itself needs to be able to tune those signals directly via its internal tuner, and third (but most important) your cable company needs to be passing the signals thru the bare cable wire unencrypted. Thats a lot of factors that need to coincide, and in more and more cities the whole shebang is unraveling as cablecos decide to take advantage of loopholes in DTV regulation to effectively force some kind of box on all subscribers. So no matter what recorder or TV you own or buy, eventually you will be tuning it via an external cable decoder box. "Cable" tuners in TVs and recorders will become about as useful as the human appendix within the next couple years.
As far as recorder upscaling goes, there's Panasonic, and there's everything else. Whatever their merits and drawbacks as usable recorders, Panasonics are known to be noticeably better at upscaling than all other recorder brands, which are a distant second at best. This is more significant re commercial DVD playback than tuner upscaling, however, and as jjeff & joed32 remarked a good dedicated player will beat any recorder at upscaling.
