Yes, wind screens are still necessary. They actually serve two purposes.
1) Shield from winds
2) Trap and concentrate heat output from the stove
Ignoring the first part 1) above, the second part is what is missed. Rather than distributing heat in a 180 degree arc, roughly speaking, it is trapped and sent back to heat the pot. As a corollary, any heat lost around the edges of the pot is also reflected back to the pot. Heat is produced in two parts: convective and through infrared radiation. Convective heating is through exhaust products and heated air that is not combusted. Infrared radiation acounts for a large portion, though.
Discussing convectition first:
I do not agree with a strict 3/4" gap around the top. This allows too much heat to be lost for no productive purpose. Conversly, too narrow of a gap will form a heat "puddle". The puddle will force heat down, into the combustion and stove. This is not what we are trying to heat, rather the pot, and what it contains, is the target. This will also increase CO production.
From this reasoning, I believe that a variable gap is needed. Depending on the setting of heat output you are using, anything between a 1/4" (on very low) to 3/4" (on high.) This will match the combustion products flow rate with their actual production. This assumes that air input is about 3-5 times exhaust output. Input is less important than output, however, so a good sized opening larger than needed will always work well. It also allows the air to cool the lower stove components.
Also, not all the heat is transfered upon contact with the pot. Some will be, some will not. Some will be picked up from the pot. This is usually carried away in the flow.
For infrared or radiative heating, using a wind screen made of aluminum or some reflective material alows the radiation to be reflected back to the pot rather than lost. Painting your pot black helps with this.
Using windscreens helps by about 25-30% given still air. In winds, they will help a lot more.