Well i am passing on indirect information that i have been told, though told by people who should genuinely know from experience and what their job entitles as to what is involved in different degrees from different universities.
Firstly, i never questioned whether economics at Cambridge was or wasn't one of the most mathematical based courses available, and so your drawing upon this is completely irrelevant as i never brought up the debate. (i agree that it is)
However, i believe that UCL and LSE do not take the same units, potentially the economic history and economic politics units that are undertaken at Cambridge, or at least not at the same time and consequently the effect is that the course would appear to become slightly more math orientated, even if not overall but at least sooner into the course.
What is 'a lot'?...if you are to pick holes in somebody's comments then make yours practical and useful...it would be fair to say most likely at minimum 50% of Cambridge economic undergraduates take further maths, but form personal research and contacts it would not appear to be as high as is speculated about particularly on this forum.
also 'those who haven't struggle'...i believe this to be a slightly broad generalisation, and if you are willing to work to understand something and give it the time and commitment you can make it work, and that is what Cambridge are looking for. If you can provide this, and persuade them so, then it is a positive thing.