Your example seems counter to common sense though!
The fact that something is a blob on the floor seems like an exceptionally good reason for adjusting the rules in that circumstance!
Much simpler to just say "no you can't knock the ooze prone" rather than try to come up with some convoluted explanation for making an ooze extra-wobbly or something
Cheers
It is however debatable how much of a place common sense is supposed to have in dnd. If we assume that the rules are conceptualized based on game balance issues, and less so to simulate a setting consistent with real-life physics, this means that we should be expected to follow existing rules, even if they don't necessarily make sense. Likewise, going with what "makes sense" may end up making the powers weaker than they were designed to be, when the DM starts imposing all sorts of rulings which restrict how well the powers work.
For example, no existing limitations were set on what a rogue may knock prone with his attacks. This could imply that the designers found nothing wrong with allowing outlier scenarios such as a rogue knocking a tarrasque back multiple squares, or tripping foes such as oozes which should normally be immune to such effects. Heck, the lack of rulings may even suggest that the designers expected you to be able to perform such stunts (how you choose to rationalize it is entirely up to you, what really matters is that you are indeed able to do it, and not shortchanged of what your abilities entitle you to achieve).
Likewise, nothing in the rules prevents me from hitting a hovering dragon with the icy terrain spell, even though the flavour suggests that it can only affect foes on the ground! If the DM rules that I cannot do such a thing, it will make my wizard weaker, because I have a useless encounter power, possibly contrary to the intentions of the designers.
As such, I disagree that this is anything but straightforward. It could either mean that wotc felt that such oddities could and should be resolved by DM fiat, or it could mean that wotc fully intended us to run them strictly as written without 2nd thoughts regarding their viability.
In fact, I agree with ac_noj that in such cases, RAW ought to take precedence over RAI.
