Tom,
I'm no expert, but as I understand it, the modern high-pressure EFI systems are considerably less prone to reversion than webers due to a number of different reasons, including:
1. High pressure - better atomization via high pressure (typically 80-100psi v. 3-5 psi for webers) makes the incoming charge less prone to condense on the walls of the throat and the runners, keeping that area leaner and cleaner - less fuel to blow back up the throat.
2. Direction/angle - high pressure fuel squirting more directly into the runner right at the back of the valve tends to keep the intake charge better contained within the runner and CC rather than blowing back up the throat.
3. Atomization/efficiency - because the atomization is so good with high pressure EFI systems, the mixture can be a bit leaner overall, making the intake charge less prone to reversion (less fuel to revert), and the mixture is better maintained across the entire rpm range (again less fuel to revert). As you probably know, webers struggle with maintaining a proper AFR across the entire rpm range.
4. Due to all of the above, modern engines with high pressure EFI systems tend to run less aggressive cams - less need to, and the buying public is less tolerant of lumpy running engines these days. People are most accustomed to an engine that runs like a Honda or Toyota, more like a sewing machine.
If you think about it, fuel dripping (or lightly pressured to be precise) into a venturi high up the intake is a pretty poor way to get fuel atomized and into the CC. It's not horrible, but it's certainly not the most efficient. And, there's no surprise some of that fuel is going to come blowing back up the intake when there's both intake and exhaust valves open all the while combustion is going on in the CC and the piston is moving up and down creating pulse waves of pressure.
I've learned/heard of the above (1-4) only from heresay and some reading on the topic - have no real first hand knowledge with it so take it with that as context. The above does make sense to me however, and I have a lot of experience with webers (and their shortcomings). While I appreciate the looks and the legacy, I have a Holley on my GT40 which says something about me. I'm also looking into an EFI weber look-alike option.
Just my $.02.