Posted 2012-January-05, 18:38
GIB thinks that the correct bid with that South hand is 3♥. If you switch the red suits, it thinks you should pass the double for penalties (why possibly play in a part score if we can punish them for overcalling?). If it didn't have good spades, it would cue bid 2♠. So 2NT is used for game forcing hands with spades stopped.
That seems to be the current logic, we can discuss changing it.
As for the lengths described by 2NT, see my previous explanation in another thread about why it's hard to get these negative inferences into the explanations. The rules for bidding 2NT are defaults that can be reached through a variety of auctions, and each of them precludes different lengths. E.g. if you opened 1♣ then you can't have long ♦, while if you opened 1♦ you can't have long ♣. But it's hard for one rule to deal with all these possibilities, so that it can specify the limits of each suit, and we don't want to split it up into lots of different rules for each earlier auction. As a result, the description ends up being vague, because we just have a single rule that says "Bid 2NT if you have their suit stopped, GF values, and a semi-balanced hand." (Actually, it's 3 rules -- one for balanced hands with 5-card minor, one for all balanced hands, and one for semi-balanced hands -- they have different priorities with respect to other rules -- so we would have to split all of them up to handle the different auctions that can lead to them.)
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