No, your curiosity is very understandable. I do teach an E fh grip for serves (for most of my students).
Here is why:
Typically a continental fh grip for serves will allow the wrist snap in the service motion. This wrist snap allows players to have a much higher toss and utilize their reach. It also enables them to hit with much more spin (using continental especially). More spin means a higher initial top speed, and a higher percentage. A win win situation right? Normally I try to teach the majority of what pro players do. However, in this case I do not. Although Becker did use this serve, its irrelevant.
An E fh grip will inhibit the wrist snap. This means the toss will be lower (better in wind), and the serve will stay very low. This serve will be flat as a pancake. It will cause the ball to penetrate the court extremely well. Obviously you will have a lower initial speed, however you will have a much higher final speed. Most people fail to take this into consideration.
Have you ever noticed that when Nadal hits a serve 131 MPH the commentators comment that it is a big serve (almost a patronizing pat on the back), but when Isner hits 131 MPH the commentators praise him? No its not because they are Rafa haters, Isners serve is much more flat. A flat serve will conserve its initial speed much better. A serve that is 131 MPH will only be 95.31 MPH by the time it reaches the opponent
http://www.donthireddy.us/tennis/speed.html. In person, you can see this drop in speed. The serve with lots of spin will have more of an arch (giving the opponent more time to react and it will sit up after the bounce. This loss in speed, bounce characteristics, and in-air-effects are more commonly discussed in groundstroke threads:
http://tt.tennis-warehouse.com/showthread.php?t=296863&page=2. In sum, Pros hit a flatter shot for the offensive put away due to the ball staying low, penetrating the court well, and maintaining initial speed.
If a flat serve is so awesome then why don't more pros use it?
Flat serves are very inconsistent. Its worth repeating. Flat serves are VERY inconsistent. Taller players are able to hit a flat serve more consistently (due to their initial height giving them more clearance over the net). This is also why tall players tend to hit a flatter ball on groundstrokes as well. In the Pros a second serve can mean certain death. Pros are able to attack second serves with ease (even well hit second serves). Have you noticed that whoever wins a match typically has a high first serve %? That is why pros do not hit super flat serves.
Why do I teach it to some players?
Very few players that I work with have aspirations to play on the pro tour. Typically attacking a second serve is uncommon for high school and rec players (assuming the second serve is hit well). I think Pancho Villas said that: "you are only as good as your second serve." This is what I teach my students. Have a VERY strong second serve. Typically, the topspin serve kicking high to the backhand (hit somewhat soft) becomes less effective at the 4.5-5.5 NTRP level. Then you need variety or need to hit it with much more spin and accuracy. Pros hit nearly perfect second serves, and they are still crushed if they have to rely on second serves. I do not find this to be the case, except in 4.5 level tennis or higher.
Philosophy
Tennis gives you a rare opportunity to have a second try regardless of your first try. Why not go as huge and risky as you can on your first try? If an NBA basketball player got two tries to sink a wide open shot, I guarantee you that 90% or more would go for a 3-pointer on their first shot.
Final Thoughts
I have had exceptions before. And when that 3.5 level player is able to crush a topspin second serve, then I obviously work on increasing first serve percentage (which is quite easy to do with a slight grip change and more topspin). Normally, until the 4.5 level, a high kicking topspin serve is almost a weapon on its own (not just a tool to help the serve stay in and keep the opponent back). Yes your first serve percentage will be bad (around 50% on an average day). However, few players under 4.5 have the ability to crush a second serve on the rise.
Fell free to ask any further questions. I've never actually typed all of this out before, so I may have skipped over some things. I encourage everyone to at least try a first serve with an E fh grip. Crush it flat and just see how your ball reacts in the air and after the bounce. Try a few with your hitting partner and see what he/she thinks, you might be surprised...