Claiming that the rotated version is wrong "because it affects more than 9 squares" is stuffing words in to the rules's mouth. It says "3 squares on a side". The diagonal has 3 squares on a side.
Please see my post above. The diamond presented is not a 3 by 3 figure, it mathematically has properties that make it, by definition, not an area of 3 rows by 3 columns.
Additionally, as I previously stated, it is not the rules' or the authors' problem to attempt to address every possible demented misinterpretation. "The rules do not say you can't light the battle mat on fire and declare victory that way. It doesn't! Therefore it's legal!"
Rather, the rules describe the area a spell consists of, and provide multiple visual examples. They say what to do and how to do it. The burden is on you to show where the rules state you should count diagonally on alternating rows and create a much larger geometric figure than is described by the rules. If you're unwilling or unable to grasp the intent of the rules, then I submit that a RPG rulebook written in plain English is not for you.
A 10x10 burst such as Maelstrom of Chaos covers an area of 100 squares, less the wizard. If you create a diamond figure of 10 parallel lines by 10 lines, and count the squares between those lines as well, what's the total area it covers?
The diamond is not a simple rotation. It's a simple consequence of the "diagonal moves take 1 square" rule that the result will be larger than a 3 by 3 square. Since that rule nowhere is said to apply to spell areas, doing so is not provided for by the rules.
You can house-rule whatever you like. But as far as I know, discussions of house-rules are supposed to take place in the house-rule forum?