On the issue of resolution - when talking solely about monitor viewing, resolution has no influence.
An image on your screen that is 640x480 pixels but saved as 72dpi, will be exactly the same size on your monitor as a 640x480 pixel image saved as 42524dpi.
The issue of resolution, only comes into it, when you are taking input from (eg scanning) or outputing to (eg printing) a hardcopy or similar.
As for the statement "The resolution of the pictures is MUCH better than any screen
captures I've ever taken too." I don't understand this. A screen capture records the image on the screen, exactly as it is presented on the screen. It doesn't compress it, it doesn't reduce its size, it doesn't shift the colours etc... Thus if it is viewed at 100% size, it will give an exact replica of what was on the screen at that time. Now, if the program does alter the screen image in anyway, then it introduces errors that PrintScreen wouldn't. Maybe it performs a sharpening routine, that makes the perceived level of detail higher (it actually is just adding errors), or there may be some artifacts introduced when it is saved to jpg. What it cannot do, is add data that was not on the screen to begin with.
What snagit does appear to have (I have just looked at download.com) is many extra features. These enable to manipulate the information that you capture from the screen (ability to do optical character recognition, capture movies etc...)