Question about PC/TV resolutions

[Wrath]

I own an iMac that can display resolutions up to 1920x1080 pixels (standard).

Out of curiosity I just switched to 720p and immediately noticed the difference with everything being less sharp and bigger on my monitor. Then I compared the result with my 6 year-old bedroom HD-Ready TV (up to 720p) by turning on my PS3 and personally thought it looked better (as in more detailed) than my iMac on 720p.

Is this my eyes playing tricks on me because I am so used to the 1080p resolution on my computer or do TVs work differently? I mean, my TV has a bigger screen size than my iMac but still gives me a better display in 720p. Of course, if I change it back to 1080p my computer outshines the TV by a great deal, no questions asked.

But how come that you can see the difference on computer monitors so easily (even it it's a smaller screen) while TVs with less than 40 inch make it very hard to distinguish Full HD from HD-Ready?

Any insight on this?