It's certainly true that you get worse mileage in hilly terrain(we have a PHEV, and live in a hilly region, so I speak from experience) but to be fair, at least some of the energy is recovered through regenerative braking. With an ICE car, none of the energy is recovered, and with conventional braking you produce more harmful brake disc dust.
But if course the mileage claims are overblown. Just like they are for ICE vehicles. Surely we all knew that....
I don't know what the mileage claims are over there, but do recall some guests telling us of 60mpg cars over there. The testing methodology here in the states is prescribed, so the results are more realistic. For example, a 2 ton SUV might have ratings like 19/27 mpg (city/highway) with a combined rating of 22 or23.
People living in rural areas will better the rating, and people in urban will have trouble matching the low side if they live somewhere that there are hills. Spouse's car (similar to above) is 18/25 rated. On highway trips (vacation, visit relatives), it gets about 27mpg at a little above 70mph. In the hills here where all stoplights are at the bottoms of hills (terrible place for efficiency, but stoplights at the tops of hills are death traps due to no view of traffic coming over the hill), the mrs. gets about 16 mpg. We live in a retail corridor (the development is just off of it), so any trip is generally met with stop lights and only a small number get to the highway.
It' be easy to complain about mileage, but it's a product of the area and use and driving more on the highway to improve the mileage doesn't make much sense (we don't drive many miles).
hybrids get close to their rated mileage here, even in the hills. Former boss of mine had a slightly smaller SUV in the same traffic conditions - hybrid. based on its rating, the gas version would've gotten about 18 mpg - he was averaging 29. The cost for hybrid at the time was $8k as an option, so it would've never paid off, but the difference in city conditions for a hybrid is stark.