After thinking about it some more, I don't think it's possible to make a direct comparison. A car is really only about fuel efficiency, horse power and a few other asthetic and enginering qualities that can't be compared to planes. Can we really compare the advancement of say car suspension over 40 years to the advancement of the auto-piloting system? The auto-piloting system is so sophisticated and advanced that a car suspension or anything else about a car can't be compared to directly. Planes also have radars, weather systems, radios and a lot of other trinkets that cars don't need R&D for. The only way to compare is something both has advanced over the years like the alloys used in plane & car construction. I'm no engineer but I think planes have become more sturdier and lighter over 40 years than cars have.
You can compare them from a "40 years ago this was the average/top of the line car, and today this is the average/top of the line car". Then do the same for airlines, and compare/contrast the differences. Whichever has more improvements over their respective spot 40 years ago wins.
IMHO cars and airplanes are about equal, with cars maybe more simply because the refresh cycles are much shorter and less expensive so there are more generations in the same amount of time.
If you care to look at some #'s:
http://en.wikipedia.org/wiki/Boeing_Commercial_Airplanes#Boeing
The 747 just past its 40th anniversary of it's first delivery (and on Jan 21 will be 40 years since it's been in service). So, it's a perfect airplane to represent the tech 40 years ago. Take a look at the tech sheet
http://en.wikipedia.org/wiki/Boeing_747#Specifications for it, and compare it to the current tech which is the 787 Dreamliner (specs
http://en.wikipedia.org/wiki/Boeing_787#Specifications).*
Cruise speeds are close enough to be the same (787:561-587 mph vs 747:555-594 mph), but top speed is actually down in the 787.
Max range is up on the 787 depending on model (787: 8,200 NM vs 747: 5,300 NM)
Total seating is down (787: 250 vs 747: 452)
Max takeoff weight is down (787: 502,500 lbs vs 747: 735,000 lbs)
etc.
So, basically the 787 can transport less passengers/weight further with higher fuel economy per flight. The real interesting statistic would be per-passenger/seat what the cost is to fly a 747 vs a 787. Obviously this isn't the whole story, but based on those spec sheets we haven't progressed a whole lot in those 40 years.
*I realize this is leaving out safety and control systems like fly-by-wire in newer systems. This is also comparing only one version, and I didn't spend the time to match up the closest spec wise. Maybe I will later.
In the car department, you have a similar thing. Take a look at the VW Golf from first produced in the early 70's to todays Golf. They have similar HP, similar MPG, still carry 5 people, etc.
What I'm really trying to say I suppose is that the only meaningful "improvements" to both autos and airplanes (commercial variants) are in regards to safety and "features". Air conditioning, air bags, ABS, powered windows/locks/steering, etc are now more common "standard features" in most cars. In airplanes you have auto pilots, many improvements in safety, etc. All of this boils down to which has a better:
Cost to transport 1 passenger/x weight from destination A to B, more safely and reliably.