Digital video: what am I missing here?

My computer has a “Full HD 1080p” 19" (I think) Dell monitor which is fed by the DVI cable in the PC (it was either that or VGA). The TV that I have connected to the PC is a 42" 720p Plasma via HDMI.

Videos look great on the TV, but look much less so on the monitor. HDMI being the reason? Well, standard websites, this board, etc…, look like crap on the TV. No, I don’t know the source’s native resolution.

I’m using VLC player for the movies, and I am using a Radeon HD 4850 graphics card. The PC is using an AMD Phenom x4 9950 Black edition, a Gigabyte mobo, and 4 gigs of RAM.

So, why do movies look better on the TV, and monitor display looks better on the PC?

The answer has to be simple, and most likely involves the video player, but I’m stumped.

What resolution are the videos you’re playing?

It could be that if they are not HD videos then the lower resolution of the TV actually suits the resolution of the video better than the high resolution of the monitor does. In a similar way, standard definition TV tends to look better on an old standard definition TV than it does on an HD TV. On a high resolution screen, low resolution video looks jagged and pixelated, on a low resolution screen it just looks a bit fuzzy.

On the other hand, the other normal PC things you look at on the monitor are at high definition and you are used to seeing them that way, so on the TV they look blurry and fuzzy and sometimes stretched if your TV doesn’t account for its rectangular pixels when displaying a PC input.