Technically, none of those spells have fly speeds, nor do they mention anything about flying when they are moved. So your DM's ruling (can cast high, but it floats down) seems reasonable.
On the other hand, 4.0 breaks down quickly when fighting in 3 dimensions. The DMG says a little bit about movement while flying, but I couldn't find anything about power use while flying.
Personally, I would probably say that zones can be moved up but conjurations couldn't - just because conjurations "occupy" a square and therefore seem to have more actual weight to them than zones, which are basically just areas of effect (that are often centered higher than the ground anyway). I don't have a RAW citation to back that, however.