Actually, not always at all but getting a sharp high def screen in a smaller area is generally harder than doing so in a higher size.
There is also the volume situation, quality, internal circuitry, inputs. Prices are silly, though you are essentially talking about designer ranges, kind of like buying something Apple.
I bought the S23a700D, its £300 vs £400 for the 750D, the differences are, the stand, normal vs the non standard type on the 750D, and I think this one has HDMI/DVI while the 750 has HDMI/Display port. Both come with 3d glasses.
A lot of 3d screens are pretty meh quality, a lot are good quality.
I just had a quick look on a fairly big retail chain in the UK, under 3d tv's the cheapest one was a 23" £270 screen, it's also NOT a 120hz screen, so I assume its one of the passive/polarisation type ones, IE, meh.
The second cheapest one is a Plasma, its £50 cheaper than the S23A750D, its also only got a resolution of 1024x768.......... honestly I swear I looked it up years ago but can't remember why plasma's are essentially low def and people still like them.
IIRC there is also a fairly hefty import duty in the UK for pc monitors, so tv's get into the uk much cheaper than pc monitors, so a monitor with a dvi/vga on it will generally cost a decent wedge more than something with just hdmi and other tv only connections like scart.
There are cheap 3d screens out there, LG did a £150 23" model, but was discontinued
You've also got to factor in though, that LG screen needed I think, the full Nvidia glasses and receiver kit which is £100-110, the £300 samsung comes with 3d glasses and has the transmitter built in.
The 750D/950D versions you're mostly just paying for the "designer" status of the screens. You can pay absurdly more for 3d TV's if you go for ones aimed at being top end designer ones, with almost identical functionality to smaller ones.