PhilKing, on 2013-November-27, 05:59, said:
1. Real opponents do not unerringly lead your doubleton - the lead is less likely to be critical when we are, say, 4333. In actual play, the stats show that "declarer advantage" occurs mainly on the opening lead.
2. Real declarers don't get 100% of 2-way finesses right or pick the correct suit to establish when they have a 4333 opposite a balanced dummy. In actual play, decent defenders drop fewer tricks after the lead than decent declarers when compared to simulated perfection, and this is particularly true on hands that require good guessing.
3. Real opponents occasionally throw the wrong thing when we run our five-card suit - these are the kinds of hands where declarer advantage still applies after the lead.
In response to the second question, without wishing to state the bleeding obvious, the fifth card is a potential extra trick.
These things may cause the simulator to be a little off center, but it's not clear that this would be a significant error. The things you mention can be true when you have a 5 card suit as well just to a slightly lesser extent.
I'm open to the possibility that upgrading is right, I'd just like a clear reason to believe this beyond something like "all the good player's know..." or "It's always worked for me" or "It's obvious that this hand is worth more than...". I get that the logistics of testing such a thing would be difficult, so like I say I opened minded on this. I do however find it suspicious that the one test I can run doesn't bear out the that upgrading is right.