You are stating an opinion as fact. Clearly there were less people there for the second game. The 90k figure is a way of falsely manipulating figures.
That's certainly true - some people didn't use the ticket they'd bought to watch the Wales-Italy match. So 90,000 does sound a bit of a stretch in terms of total attendance for Cardiff (although more people than I expected watched both games).
But what's the alternative? It just so happens that two games took place last Saturday, but in the same stadium. That shouldn't somehow invalidate people's attendance for each game. What if exactly the same people go to each of the games at Leeds - should they not be counted simply because they have two seperate ticket stubs?
It's not a perfect system, but the final cumulative figure will be pretty close to the number of people who attended individual games at the end of the world cup. The same people will no doubt be counted multiple times, but there's just no way round that.