This is kind of a side note and inspired by JMT's note that the 42" widescreen TV's at the store felt roughly the same size as his "normal" (ie. 4:3 ratio) TV at home.
I'm tackling this as a math problem where we want to maximize surface area (big screen baby!) but still want to get a new HD screen (ie. 16:9 ratio).
Hypothetically, let's consider any rectangle with a fixed diagonal because that's how we measure TV's... by their diagonal size. To maximize the surface area of a rectangle with a fixed diagonal size, you've gotta make the 2 sides as equal as possible (ie. a square). But HD, though it uses a ratio that is more comfortable to watch (at least for me), makes TVs more "rectangular", making the 2 sides significantly different lengths compared to our old, normal TVs where the sides are close to the same size. Therefore, when comparing 2 televisions, an HD TV (16:9 ratio) and an old, normal TV (4:3 ratio) with the same diagonal size, the HD TV will actually have signficantly LESS surface area (ie. the HDTV will be smaller).
I'd been thinking about this problem for a while so I thought I'd tackle it with some numbers. I've done some calculations to try and back this up for the more mathematically inclined of you:
Comparing JMT's 27" TV to 42" Widescreen
a=unit length of TV
c=diagonal of TV in inches
d=surface area of TV in inches^2
(4a)^2 + (3a)^2=c^2 (using your normal 27" screen which has 4:3 ratio and using pythagoras)
16a^2 + 9a^2=c^2
25a^2=c^2
c^2=27^2=729 (sub in 729 for c^2)
25a^2=729 (divide both sides by 25)
a^2=29.16 (square root both sides)
a=5.4
So each side of 27" TV is 4a and 3a
4a=4(5.4)=21.6
3a=3(5.4)=16.2
Surface area of 27" normal 4:3 ratio TV
4a(3a)=21.6(16.2)=349.92 inches^2 of surface area
Using 42" Widescreen Television with 16:9 ratio and using pythagoras
(16a)^2 + (9a)^2=c^2
256a^2 + 81a^2=c^2
337a^2=c^2
c^2=42^2=1764 (sub in 1764 for c^2)
337a^2=1764 (divide both sides by 337)
a^2=5.23 (square root both sides)
a=2.29
So each side of 42" TV is 16a and 9a
16a=16(2.29)=36.61
9a= 9(2.29)=20.61
Surface Area of 42" widescreen 16:9 ratio TV
16a(9a)=36.61(20.61)=753.76 inches^2 of surface area
Conclusion
Nope, turns out 42" widescreen has more than double the surface area of a normal 27" TV!
Comparing 42" Widescreen to 42" normal TV
(calculating a^2)
25a^2=c^2 (regular screen)
337a^2=c^2 (widescreen)
(calculating surface area)
12a^2=d^2 (regular screen)
144a^2=d^2 (widescreen)
Using 42" Normal 4:3 ratio TV
c^2=42^2=1764
25a^2=1764
a^2=70.56
12a^2=d^2
12(70.56)=846.72 inches^2 of surface area
753.76/846.72=0.89=89%
Conclusion
Turns out at 42", the HD TV will be only 89% as big as the normal TV of the same diagonal size. And the problem will only get worse as you get bigger TVs!
