The signal issue does exist, but I believe it's more down to how phones are rigged to report signal strength.
It seems you'll get four or five bars across a huge spectrum of signal strengths, it's been rigged this way for years as that's what the networks want. As soon as you get down to three or two bars things are getting pretty sketchy anyway.
I'm sure when the Apple engineers were testing it the found;
With no physical contact, or a case, antenna performance was better then iPhone 3.
With typical physical contact antenna performance was on a par with iPhone 3.
With full interference contact antenna performance is marginally* less than iPhone 3.
Their conclusion, on balance, probably was to go with this design - typically it out performs iphone 3 and offers an innovative form-factor. Of course their conclusion did perhaps not allow consideration for mass hysteria relating to Apple products and every dweeb in the world with a twitter/blog deciding that they are an RF engineer.
Anyone know why they didn't laminate the aluminium, would of thought you could make the problem go away - guess not very durable. Anyway I'm sure someone will be selling $3 kits which allow you to apply a laminate to the antenna soon.
*marginally to be defined.
I'm looking forward to the class action lawsuits by lefties.