I can't say if the 700 has been discontinued, but I'd say that it's availability has been curtailed. I think to spur more sales of the 800. A lot of people were skiddish of the automatic load control and non-deep rinse, even though you can defeat the spray rinse only feature by turning the control to "fabric softener". As a result, customers turned to the 700 series who would have otherwise gone TOL. I also think the 800 may have been over-priced to take advantage of its energy efficient rating.
There was one 700 model recently at the outlet store in dark navy blue metallic. I'll check it's stock number and see if it is still available.
I don't know what the differences were between the 600 and 700, but knowing Sears, they probably were not hugely significant.