Sure monitors have been "High Definition" for a long time, but I definitely wouldn't call them HDTVs (which is what we are talking about here). How many people do you know with 16:9 (or even 16:10) CRT monitors and out of those ones, how many have TV tuners in them.

 Surely thats more than a little bit dangerous!

 That pic is dishonest, it exaggerates the difference between HD and SD far too much.

I play my X360 on both SD and HD (including the game on the first pic, Kameo) and first, Ive never seem those ugly horizontal lines like on the SD pics above, and second, the lighting/gamma is totally messed up on these SD screens while in reality it is slightly better on SD (because they are CRT TV-screens).

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While it is to the extreme, this is the comparison most people will be making. They'll have their old SD CRT tv (with those ugly horizontal lines) and are probably running over composite cable, so the colours are totally messed up too. SD on an HDTV over HDMI or Component is automatically a massive upgrade to their CRT, even before they turn up the resolution to HD.

I think this one is a good example.

what is the deal with the standard definition side being smaller and sized oddly? I know the HD is widescreen, but it doesn't make a good comparison picture.

 This is a great example, far more honest than the ones above that had all kinds of weird artifacts.

SD simply feels more "blurry" just like in that picture, but colors, lighting, contrast etc are rufly the same as in HD (often even better if we're comparing CRT ("old TVs") with LCD HD-TVs).

To be honest, console games on SD-TV look far better than running PC games at for example 800x600 resolution on an LCD screen (and almost as good as 1024x768). The "blurriness" on CRT (normal SDTV-sets) sort of compensates for the lower resolution to some degree so that the picture looks less pixelated... but I dunno if anyone here has noticed that or agrees. Also, plasma screens are better than LCD to make low game resolutions look decent.

Simply put it's taking into account what you'd be able to put on the screen while still keeping everything the same distance. The distance of the picture doesn't change, the ratio of the displays size does.

Edit: Of course, 16:9 is not limited to HD an you can find some 16:9 displays that are not HD however most are 4:3.

That is actually pretty accurate.
the horizontal lines are there because the SDTV where that pic was taken from uses interlace.
480i i meaning 480 interlaced vs 1080p p meaning progressive.
If you don't believe me, take a picture of your SDTV and HDTV, you'll see the same results.

Of course a still image exacerbates the lines, because the TV refreshes at a fast enough rate where the naked eye would have trouble distinguishing the lines unless the person is sitting very close.