HD ready concerns the ability of television receivers to display high-definition pictures. In the USA, "HD Ready" refers to any display that is capable of accepting and displaying a high definition signal at either 720p, 1080i or 1080p using a component video or digital input, and does not have a built-in HD-capable tuner.
The fact that a product bears the label "HD ready" does not necessarily mean that it can display the full picture resolution possible from a HD source. Most HD-ready sets do not have enough pixels (1920x1080 or 1280x720) to give true pixel-for-pixel representation without interpolation of higher HD resolutions.
BASICALLY, you want your TV resolution to be no less that 1280x720. If it is less, return it. If it's that or better, you're good. You'll just need to add an HD tuner/receiver before subscribing to HD channels.
Past that, to say that "You can't see the difference between HD and regular resolution on any TV that is less than 42 inches" is complete garbage. I have a 34" widescreen HD Sony Wega and TRUST that you can tell a difference with the HD. Ask anyone that has HD or works with HD TVs if that above statement is true and they'll tell you that anyone who thinks you have to have a 42 inch or larger TV to enjoy HD is a moron.
Hope that helps!
Edit: I just read that the power button on many Samung TV's is not actually a button, its a small touch sensitive zone. So though you may not see it in the product pictures -its there.