I agree. Not every situation needs to be resolved by some established formula. Long before skill systems were part of D&D a good DM made situational resolution calls that made sense at that particular moment.
For example if the party were being chased by a beastie that would probably kill them (and the party suspects as much) and ends up in a dead end corridor with a stuck trapdoor the DM might decide that an adrenaline surge might allow the fighter to combine his STR and CON attributes into a check to get the door open perhaps at the cost of a few HP due to the strain.
This doesn't mean that every stuck door can be tackled that way from now on. The fear of certain doom was a catalyst for that effort which might happen again at some point but not on demand.
Not only that, but if you do not make situational rulings, all that can happen within a given situation can automatically happen during any other like situation.
As a quick example, in a cave system with a damp, sloping floor, as the GM I am allowed to say that there is an X chance per round of slipping, and these are the results. In another situation, I am allowed to call for a Balance check. In still a third situation, I am allowed to call for a Reflexes save. This may, or may not, be tied into unusual features of the area.
Part of the GM's job, IMHO, is to decide within a given encounter area "What could happen? What would be fun? What would be interesting?" Each encounter area can have its own rules based on the answers to those questions.
The rules may have no provisions for a horse going lame, but a horse going lame may appear on the encounter tables when crossing Armadillo Plains, due to the many armadillo holes in the ground.
Likewise, a specific staircase can have a 1 in 6 chance that anyone travelling on it for the first time will trip (check until a trip occurs). The effects of the trip are X. Characters can prevent or modify these effects with Y.
One pit might be avoidable with a Reflexes save, DC 15. Another might require a Reflexes save, DC 50, to get to the edge in time, because it is a bigger pit. In both cases, the GM may offer the players a choice between a Reflexes save to avoid falling, or an Acrobatics check to reduce damage. Paying attention to the description is needed to guess which is more likely to be effective.
Sometimes the "bad thing" that happens may be a "good thing" in disguise. Falling means that the PC sees a crack in the stair which conceals....
something.
Situational rulings allow
anything to happen in a game. They also require the players to interact with the setting as
setting, rather than just as a rules structure. Both of these are, IMHO, very, very good things.
YMMV.
RC