Hi Jean Olivia.
As you know, it's always nice to look at "Jerry Springer" or "Ricky Lake"
when we play our keyboards....

Seriously, what I've seen is that the TV-out is used to sendt lyrics to a
TV monitor. Other keyboards as i.e. Ketron SD1 already have it, and it is
a common way for artists to read the lyrics these days. Besides of that,
you can also use the keyboard as a karaoke-machine when play the midifiles
with lyrics.

USB is a newer and faster way/standard to connect the keyboard to other
hardware equipment such as i.e. a PC and CD writer etc.
If you see a cable among your PC stuff who have a "little square thing
with a hole in the middle" in the end of it, and not a lot of pins or
small holes like the "old" printer cable, it's most likely used for a USB
connection.
"Firewire" is also mentioned regarding to faster "lines" between different
equipment as a competitor to USB.

The KN6500 is better sounding than a KN5000, and a KN7000 will probably
sound even better, as every new model in the future will.
They call it evolution, or is it development, and as long as there are new
models coming, there will always be new things to tempt us
I guess it's only the personal needs and bancaccount who deside if it is
"nessesary" to upgrade.

The NX sound is a "Technics thing", and are not comaptible to GS as far as
I understand it. GM2, GS and XG (Yamaha) is a extended function to General
Midi who give the users some more possibilities than standard GM and now
the two "big guys", Roland and Yamaha have an agreement on that they will
make a common standard out of GS and XG for a new "world midi standard".
256 voices instead of GM's 128, more flexible sound parametres etc, etc.

The weight?
My guess is that they are trying to keep it as low as possibleb but if it
increases like my weight have done lately, I'm afraid it's not going to be
too easy to carry around anymore....
GJ