There are two issues here: air recirculation and high airflow (which increases convection).
I happen to be a huge airflow-fanatic. I did not truly get control over my roasts until I began to understand airflow and the influence it has on roasts. Jim, you are correct that most specialty roasters use drum roasters, but drum roasters are engineered to have very different airflows from each other, and many roasters modify their roasters (as I have) to maximize airflow control. This gives the roaster control over convective energy, the most powerful force in the roaster's arsenal.
One of my three roasters is a Roure, which has a perforated drum and a power burner, and baffles at both the air intake and output that allow me to tightly control airflow. I can therefore make the roaster behave like a Probat (relatively low airflow) or crank the airflow up to where it acts almost like a fluid bed (it is possible to get 7 minute full-batch roasts on this roaster). The nice thing about moderate-to-high airflow is the coffee is much cleaner and clearer; this roasting style is well suited to crisp, floral, clean coffees. With lower airflow I tend to get enhanced molasses-type flavors, which works for other coffees. Our Renegade has intentionally lower airflow, which helps develop sweetness and dusky intensity, useful for darker roasts and low notes in an espresso blend. On my Samiac, we use both baffles and an inverter-controlled blower motor to tightly control airflow. Again, high airflow=crisp and clean (and shorter roasts, frequently), lower airflow=sweet and complex (and longer roasts). Of course this is very oversimplified....however it is consistent with the observations you mention.
I do think that putting all drum roasters in the same category is painting with too wide a brush. Fan size, blower speed, and perforated vs. solid drum construction all drastically change the behavior of drum roasters. I would say that each roaster design (and every roasting machine modified by tinkerers like us) occupies a different place in the airflow continuum. I think of it like this: since all roasting machines balance radiation energy transfer, conduction tranfer, and convection transfer, each unique machine has its own fingerprint (frequently controllable) as a balance of these things. This gives each roasting machine its unique personality. The conscious roaster is keenly aware of these variables, and seeks to control (and sometimes profile) each variable. It gets complex, but once you master it you gain true control over your coffee.
Now then, recirculating is another thing entirely. It is ridiculous that we do not recirculate air in most of our roasters, it is a big waste of energy. Most roasters are using the equivalent of Model T technology to roast their coffees. There are real problems reusing smoky air to roast with, but I believe the Loring technology is sound and I taste no artifacts of smoke or combustion byproducts in the coffee. This is the wave of the future.
The high-airflow bowl roasters are interesting, but there is no reason a roaster cannot gain the same control by using a properly designed (or redesigned) perforated drum roaster, or even a solid drum roaster (given the right configuration of burner(s) and fans).
Specialty Coffee Association of America