Apple has admitted that if you hold the phone across the break on the left band, that reception is diminished. They say don't hold it that way. They claim all phones diminish reception if you hold them at the bottom. That is true, but not on the same scale as the iPhone.
In the Anandtech review, while being held naturally, the NexusOne lost 10.7 db while iPhone4 lost 19.8. Thats a drop of 9.1db. As a frame of reference, 10db is a 10x change in signal strength. 9.1db = 8x lower signal strength.
There was an uproar over the Nexus One's performance. Google never really addressed it. And you can see what a wild success that phone has been.
I thought people bought the iPhone because its the best, not because you can find one phone somewhere who's performance is ONLY 8x better.
Meanwhile in their test, the iPhone 3GS lost 1.9db, meaning a drop of 17.9db. For reference, 20db is a 100x change in signal strength. At 17.9db difference = 62 times weaker signal strength.
FYI. db is a relative measure. If you want to find out how many times different two value are, and have the db value, the formula is:
10 ** (db/10)
In words, 10 raised to the power of (db divided by 10).
So for a 17.9db change, thats
10 ** 1.79 = 62 (rounded)