vented combos, condenser combos, blowers .....
aussie-plug, you're right : once there were some german combos without blower (I guess made by Lepper and badged as Matura, AEG and Bauknecht). To be effective they had to heat @ hightemp and clothes yellowing was an issue.
In the meanwhile there were vented combos as these Philco/Bendix and the GHIBLI made by SANGIORGIO in IT
These saved water, but not paint & elbowgrease : one had to keep windows open while drying otherwise the room had to be painted every 6 months. The only vented combo with an exaust pipeline is that old Whirlpool in our Webmaster collection.
The solution to both issues was a condensed combo with blower.
Consider also that usually combos are bought by those who haven't much place and haven't a vent in the wall
I had a Candy 16 WD blower/condenser combo. The slow spin speed 570 rpm caused it take centuries to dry, waste plenty of power and water .... to dry
Today Miele makes the W2670 combo than uses 9 litres only while drying. BTW I'd never buy it : separate miele washer & dryer are much cheaper and faster.
Dryers
once they were vented only;
here (IT) dryers started getting popular in the last 5/6 years,once we had rare zanussi vented ones
That's why we've only condenser D, while in northern EU still there are vented ones (houses have proper vent in the wall behind the D), that are more energy-efficent
Latest D have an heat pump inside : the hot side warms the air to the cylinder, the cold side is used as condenser.
This cold condenser is so more efficent than usual air heat exchanger, that heat pump dryers are A rated (best energy savings)