I think Midrar meant to say that with ISY you can create a virtual limitless and intricate set of programs that run without a dedicated computer. Scenes that run wihtout some sort of controller always execute the same, so with an ISY or computer you can have scenes that run differently based on any number of factors (like time of day) or run on their own.
ISY is a very powerful tool. A UPB firmware is in beta for it right now so I think if you want to use ISY, you could go either way (Insteon/UPB).
Insteon is the only dual band product right now where all of the most common devices use RF and powerline (or you can spend less and get the power line only stuff).
14,000 sf is a big home but I really doubt that you would have trouble with Insteon or UPB. The RF only products I suspect would not work very well, especially if the home is spread out. I have 6500 sf with three boxes and the powerline only Insteon stuff (installed it prior to the dual band, I would use dual band if doing it again). I rarely have a failed command but would bet anything that it is powerline noise that is the problem, not size of home.
If you have a "green" spirit in you (which an odd number of people with gigantic homes seem to have), you might consider power consumption of the devices. The current Insteon switches consume well under 1 watt per switch. Check out IndyMike's thread on that. If you are going to install 150 or more devices in such a large home, that can add up. I don't know what UPB eats per switch and it might differ by manufacturer. If you can't find a thread on that you might consider buying a few of the switches and a killowatt and testing it yourself.
The current Insteon switches also have a beeper in the switch which, to my knowledge, is unique to them. I have found it to be a nice feature which I initially couldn't see any use for.
Anyhow, if you are really going to automate such a large home, it would be well worth your time to buy 3 or 4 of each type and play with them. You can always unload the extras on ebay. Also read up on the controllers like ISY and Homeseer.
Also, I hope you have a lot of time to play with it. Automating that large of a home will present you with a myriad of options and, if you really enjoy this stuff like some of us here, you will want to take full advantage of it, which means lots of programs.