LeQueen, I used to think as you do, but I now think that's too simplistic & am agreeing more with MissAnne.
The exams may be a little easier (I do think sciences are and maths a little to be fair, but not hugely so and they are aimed at a much wider audience), but my observations are as follows:
Maths: I did no calculus in my O level maths (there was some basic calculus in A/O additional maths though, but not too much - no more than is in the current iGCSE which really isn't all that different to GCSE in difficulty in spite of the hype). You do have to do one GCSE paper without a calculator. Overall the exam is a bit easier than the old O level, but not hugely so.
English: I remember being really, really bad at English and still got B (lang) & A (lit) at O level (lang taken a year early). That was in spite of being banned from using commas entirely and instructed to stick to very simple sentence structure only. The level of my ds's GCSE English essays and analysis has astounded me & is far beyond what we had to do (it may have been a bit beyond what was needed for GCSE too, I'm not sure). So I really have seen no evidence of English being any easier.
Science: Well I do think this one is a bit lamentable, but a fair bit of the problem is not comparing like with like. The core science papers are (imo) laughably easy, but that is the easiest of 3 stages of science papers. I can say that the Physics syllabus at least is very reduced though and the questions are more predicatble/straightforward though even at the higher end. This imo is the area where bright youngsters today are not getting enough challenge (too many getting not just A*s, but not dropping any marks at all), but again, nowadays everyone does science, whereas in days of yore it was only the scientifically inclined who chose more than one (usally Biology) and of course only the most able sat O levels anyway, so maybe the 'dumbing down' here does have a greater good in terms of scientific awareness in the general population.
I do agree that the very, very ablest aren't especially stretched at GCSE, but it's getting more common to do them early or AS levels alongside to compensate for this, so it's not a huge issue and as MissAnne says they're actually not all getting straight A*s in the main, so there is still just about enough differentiation at the top I think.