Yeah, that sounds a bit defensive doesn't it?
Point is, he isn't arguing a general case here but a very specific one. A theta join like yours is will involve half the number of rows a Cartesian product would involve.
Code:
Rows in Table A Rows in Table A Cartesian Theta
2 2 4 2
20 20 400 200
200 200 40000 20000
2000 2000 4000000 2000000
20000 20000 400000000 200000000
There is a calculable and exponential increase in the number of rows processed.