ryan,
I'm not good with words at times, but I will try to describe what delroy was referring to. The purpose of a jointer, as you already know, is to achieve a "FLAT" smooth board surface. If your extension is the least bit high, you will snag on the extension outfeed during the run. If the extension is the least bit low, you will most likely tip toward the front during the run. This will make it difficult to get the "FLAT" surface you want. My floor jointer is only about 48 inches which only gives me about 24" inches on the infeed and outfeed ends. Any board I run over 2 feet has to have extreme care as it feeds. Any machine shorter becomes that much more difficult.
Yes, weight is a good thing, but the table length is the most important factor of this tool. You need as long, flat and smooth surface as you can get to achieve a good pass.
I would love a 16 foot jointer if there were such a thing
If I have not made myself clear, perhaps one of the other members can translate this better for you.
Cheers