Actually the iPhone 4 has the best antenna DESIGN available. By using the stainless steel band, you give the phone a professional and appealing aesthetics AND give the antenna more direct access to radio signals.

What Apple did wrong was put a cheap/inferior receiver/module compared to the norm:
since the design should've allowed for better signals, it would have to be a bad software stack (i highly doubt) or antenna that is weaker ... to bring the reception quality down (even when you aren't touching the bridge)

(actually you can, continue reading)

And another thing Apple did do wrong was put the bridge in the wrong spot. If they expect people to use this without sticking duct tape or having to put a case on.
I am right handed so I probably wont cover that bridge while on a call. But if I have to multitask (jot a note etc) I will change hands and now cover the bridge.
If they put the bridge on the top or bottom, there would be an issue of dropped reception when holding the phone in landscape (horizontally). For instance, streaming media while playing games or watching videos (multitasking) or even streaming videos ... I will still be bridging the two bands.
So where to place it?
On the left or right side on the the top (near corner).
1) I won't be touching it while holding the device in landscape (TICK).
2) I won't be touching it while holding the device in portrait (small tick) ... while people can shift the phone down from the usual grip position to accidentally bridge with the inside of the index finger medial phalanges. But the incidence would be much lower and users wouldn't need to but could easily adapt to avoid the issue.

Win, Win?

No!

As mentioned earlier, this places the antenna much closer to your central cortex (brain) so there is increased radiation danger.
It is all about compromises.

1) Go with the inferior but proven design (Nokia, Samsung, HTC etc)
Design= Mediocre reception, Mediocre radiation, Mediocre aesthetics
2) Go with the iPhone 4 design and lose reception
Design= Low reception, Mediocre radiation, High aesthetics
3) Go with the iPhone 4 design and destroy the design by placing a duct tape or use a phone cover over the bridge.
Design= Mediocre reception, Mediocre radiation, Low aesthetics
4) Go with the iPhone 4 design but have a large plastic/non-conductive material placed where the bridge rests by the OEM
Design= Mediocre performance, Mediocre radiation, Mediocre aesthetics
5) Go with the iPhone 4 design but place the bridge on the top left (or right for left handers) corner
Design= High performance, High radiation, High aesthetics

Ofcourse, these are some possibilities, the OEM may choose to tweek the actual antenna and design to make it more appealing, or less radiation to people, or better reception than what is inferred.

If I was designing a slate phone (like the iPhone) as a user:
My first choice would go to numb 5 if the radiation level was acceptable.
Then numb 1, I want a universal design, not areas where the aesthetics looks poor
Then numb4, it may not be the best but it is acceptable and gives a universal design
Then numb 3, poor aesthetics but good reception is better than no reception
Then numb 2, ppfffh!