[Lazy loseth fails to read through whole thread, running the risk that he may simply be repeating what others have said.]
I think it's important to keep in mind that there's a difference between A) a standard and B)what adventurers would normally carry. If adventurers continue, in 4e, to be super-rich and continue to have a need to cart around all or most of their wealth with them, then I'm sure they'll prefer gold over silver, and magic items over both as their main form of transportable wealth. Nothing wrong with that.
But, for me, the 'standard' is what the world functions in: what people quote prices in, what items are listed in in the PHB, what orcs demand as tribute, what shares in merchant operations are denominated in, what barons count their revenue in, etc. In the real middle ages, this was always silver. Not copper, not gold--always silver. 'One pound' (i.e. the ancestor of the currency still used in England) was a virtually universal denomination of money throughout former Roman lands and it meant, literally, one pound of silver. Now, just because your salary was, say £12 per year, that doesn't mean that the king would show up to pay you with 12 coins. In fact, most of the time, no pound coins actually existed--it was just a money of account. The king might actually pay you a dozen gold nobles, two or three bars of silver, a few dozen silver marks, a hundred pennies (a silver coin in the middle ages) and a few dozen farthings (a quarter of a small silver coin), but instead of that mouthfull, he'd just say, 'here's your twelve pounds, Castellan; don't spend it all in one place.'
That's how I like to think of money in D&D: gp, sp or whatever represents a money of account (and an average weight), but what someone actually pays when they buy a 60gp sword could be any old mish mash of coins and pieces of metal. This is true of a non-POL setting, and even more true of a POL one. The only thing I'd like to switch is to have the base unit of account be the sp rather than the gp. Or, even better, give the 'sp' a more thematic name, like 'mark.' Or maybe divide all prices by a factor of ten and make the base unit the pound. Swords might cost £5 and a warhorse £20. Then a gp could be a coin worth one pound--it would still be a gold coin, but would represent one pound of silver. This way, the standard could be silver, but adventurers could still carry around their precious, low-weight gp. But in any case, however it's accomplished, a silver standard just gives me way more of a medieval feeling, which I really like in my D&D games, POL or otherwise (I realise that this isn't to everybody's taste, though).