Yes, ensuring 1:1 is important. Think of it this way:

While the display may say 1080p capable, it's possible it doesn't have a 1:1 mode to ensure all 1920x1080 pixels are actually visible. Instead, it may be doing 1880x1040 actual visible pixels, meaning it's running a 40x40 pixel overscan.

LCDs and plasmas can also be tricky, since many use some off standard resolutions. The 26 inch LCDs we have here run at 1366x768 visible, and so we have to set the PCs attached to them to that odd resolution to get it to fill the screen and not scale. They will do 1280x720, bit it's clear it is scaled when looking at a windows desktop.