There's a lot of good advice here, but I think there's some grey areas I can add to.
1) While I agree the collet bushing was the "defining" characteristic of the '70 Series, it did appear on both pre-70 guns and 80 guns. Huh?
a) in 1968 and 1969, Colt sold and tested limited numbers of "BB" guns. These were serialized in the standard "C" range like other commercial pistols, but were equipped with the collet bushing and were suffixed "BB" on the serial number (
barrel
bushing). These show up from time to time, so if someone tells you they have a pre-70 collet bushing gun, they MIGHT be rigth, but these guns are rare.
b) Colt used the collet bushing for five to six years after the introduction of the 80 Series (1983). They did not stop using it until 1988/89. Thus, the defining feature of the 80 is the firing pin safety and not the lack of a collet bushing.
2) Trigger pull:
a) Weigth: I've done some tests various guns and have found a range of additional trigger pull added buy the f.p. safety system ("fps") to run from six to 10 ounces, with an average of 8 ounces. So, if your fiinger is calibrated to the ability to distinguish 1/2 pound or less, you could tell the difference if you were to compare a single gun with the system installed or removed. But it won't be readily apparent between random factory guns as there's that much variance overall between guns, and also between a new-ish gun and a well broken-in one.
b) Creep/feel: I believe most of the slam on the 80 fps was because of a general increase in the average quality of the trigger in the guns between the '70s and the late '80s. Most stock GM's, Deltas, and CE's I've sample or own that were still stock and made from '87 to '97 tended to have creepy triggers. I have personally experimented and my conclusion is that it was attributable to the hammers and how they were machined. Taking out the stock period 80 system hammers and putting more modern ones or older ones made dramatic improvements.
So there's some more fodder for debate. To address the very first question, though:
Im just wondering what the differences are between a Colt series 70 gov model and a Colt series 80 gov model.
If you take a first year Series 80 GM and lay it next to a last year Series '70, you are going to find only TWO differences:
1) different cosmetic roll marks on the slide
2) the presence of the firing pin system.
Those are the only true "changes" because of the introduction of the 80 Series. Other differences you might find came because of ancillary engineering changes down the road, and there have been a lot of changes since then. The current production guns coming from Colt have fantastic, light, crisp triggers whether pre-80 (WWI models, Series '70 re-stamp) or 80 fps style (1991 models, XSE's, etc).
So that's what that little bar thingy, with the oblong hole in the middle is I had left over after I put my 1911 back together.... 
I can't believe I left the disconnect out of my explanation.... Sheer hurried stupidy, that's what I get for not proof reading my post. 