I've got a 99 1.2 Punto 60 and it will top out at about 100. I woudn't be too worried about the fact it tops out in 4th - I work for a transmission design company and when I started I was writing specs for vehciles that top'ed out in 5th. The problem is, the car companys want their cars to have a cruising mode for the motorway with good fuel economy so they can fudge the results of the road-tests for magazines. The last car I did was a forthcoming supercar and I'd planned it to do 220 in top, but the car company told me I had to top it in 5th, so now it will just about make 200.
The other thing is, as you go higher in the gears there's less torque at the wheels, and torque means force, and for a given weight of car less force means less acceleration. What that all means to you the driver is that when the car is near the limit of drag equaling drive force you may still be accelerating, it'll just be so slow you won't notice it. The manufacturer's top speeds are on big high-speed banked ovals (like NASCARs use) so they can drive at really high speeds for miles and miles, letting the car reach a higher top speed than you can reach on a normal road.
As to the 110-downhill fully-laden thing, if you load a transit van up with sofas and drive it from Southampton to Banbury along the hilly roads you can get it decently over 100 (which is not possible on normal roads). The extra mass is giving you more acceleration.
Hope that made some sense.