I can tell you that there has been no change in procedure calling for earlier extension of the gear.
As you probably know, most jet aircraft will not decelerate and descend at the same time (At least not very well - the 727 and DC-9 seem to be exceptions). The 757, for example, is so aerodynamically slippery that it's pretty normal to have to use either the speed brakes or the gear to help come down and slow down. For example, say you're coming down on the approach at 230 knots and flaps 1 and DEN approach asks you to slow to 180. Guess what: you're gonna need the drag from the gear to help you slow down while staying on the glide slope profile.
For safety, UA and other airlines fly what's called "stabilized approaches". While each airline uses their own criteria, the concept is to have the aircraft on speed, engines spooled, and in full landing configuration by a certain point on the approach. At United, it's no later than 500' in visual conditions or 1000' in instrument conditions. The gear must be down and final descent checklist complete by the outer marker (instrument conditions) or by 1500' (visual conditions). Not having these things done means a mandatory go-around, and UAL has really been emphasizing the "stabilized approach" lately. The pilot has to work backwards from these numbers to figure out where he should start slowing to make the approach come together by this point, and DEN seems to be a little tricky for a few reasons:
Higher airport elevation means higher groundspeed;
When landing to the south there's sometimes a quartering tailwind pushing you towards the runway, and;
DEN approach usually keeps arriving aircraft high on the way into the airport before cutting you loose on the approach.
For all of these reasons using the gear farther out than normal helps slow the airplane down AND bring the plane down to proper altitude to be stable by the above limits. You could also use the speed brakes in some airplanes, but the gear is usually more effective at dragging the airplane down.
Using the gear early also allows you to keep the speed up longer. The UAL 757 flaps 1 speed is 230 knots, but you can throw the gear out at 270. Rather than start slowing to 230 or so 20 miles out and then feeding in flaps, some pilots like to keep 250 knots until closer to the airport, then drop the gear to drag the aircraft
down to approach speed by the above limits. It's all technique.
Just a few guesses off the top of my head.