True - but mostly because of technological change. Put simply, the design of aircraft air conditioning systems has become more sophisticated over the years.
The air is bled from the engine compressor (so it is hot from the compression) and mixed with colder air to provide the requisite temperatures throughout the cabin. This engine air bleed is at a cost in terms of the engine performance and hence fuel consumption. To reduce this cost, a large amount of the conditioned air is filtered and recirculated before eventually being dumped overboard. There are two main valves which control this and the aft (rear) valve opens slightly more than the forward valve to promote an airflow from front to back through the cabin. This is largely historical, dating from when smoking was permitted, and ensures that the smoke got carried overboard through the aft outflow valve. The banning of smoking has permitted modern aircraft to employ recirculating systems to reduce operating costs.
Cheers
Dave (flying big jets since 1972)