Unlike your Civic, the Volt has to lug around a huge battery, a complex powertrain, and two high-torque motors. Its curb weight is about 40% higher than a 2008 Civic.

BTW, did you mean a Civic Hybrid? Because the US EPA estimate for even the most frugal of 2008 non-Hybrid Civics is 29 MPG combined. If you are driving so as to coax 50 MPG US out of a 2008 Civic, you will love the Volt.

Since he mentions the UK I assume he means the diesel version which is estimated at 60MPG. The latest version of that car is estimated to come in around 78MPG.

I think you're using highway-driving only. The estimate for the latest Civic I could find (2012) is 67.3MPG UK (55.9MPG US) combined, using a British cycle. This is diesel, which has a higher energy density than gas, so the equivalent in gas would be 49MPG. But also note that european MPG measurement cycles are much more generous than US ones: the EPA measure would be much lower in the US.

All in all the Volt probably is almost the same as and possibly better than, the Civic in gas-only driving, despite the fact that it has to lug around an additional electric motor and battery.

Sorry, should have mentioned - it's a 2.2L diesel.

But on the other hand...

My 1994 Nissan Sentra got 35-38mpg and my 2001 VW GTI (with a V6!) is still being driven by my bro-in-law and gets 30mpg highway with 260,000 miles on the original powertrain.

The fact is that cars are far more complex, far heavier, and have bigger engines today than they used to, at the expense of gas mileage.

That's the gas only mpg, which is a near useless metric for a plug-in hybrid. In my use-case I would almost never burn gas in a Volt. The 2016 Volt gets 53 miles on battery alone. That's what I drive during the entire work week. Considering you would plug this thing in at night, typical buyers would almost never be using the gas engine.

You need an apples to apples comparison. Many people claim to get higher MPG than the car's official ratings. You can't directly compare your own experience with the standardised MPG testing. As you say, traffic and driving affect it. Maybe the car would get more than 42mpg with your driving conditions.

You might be thinking about miles per UK (Imperial) Gallon, rather than US Gallon. 1 UK gallon = 1.2 US gallon. Even a new 2015 Civic only gets around 32 Miles per US gallon.

A) Civics are generally regarded as having very good mileage.

B) Civics weigh 500kg less.

C) Again "on gas alone" which is not the expected mode for a Volt

A yes

B So? That just means their car needs to go on a diet. If those extra kg got us something then you might have a point.

C The point is to maximize distance traveled per energy used while providing decent range and carrying capacity. The point isn't to build systems that have a lot of downsides(complexity and weight) for no benefit.

those extra kgs get you 53 miles gasless.