I don't think ISB or PGPX or PGPEX will be automatic choices for people with 4 or 5 or more years of experience. There are +s and -ses in choosing the one-year programmes over two year programmes.
One year programmes tend to be more general mangement type and the number of electives one takes in a one-year programme will be usually significantly less than in a 2-year programme.
If some one wants to specialize in finance etc, they may be better off doing a 2-year programme.
Also the job opportunities in consulting and Finance are much better after doing the 2-year programmes in IIMs, particularly A, B & C, than the job opportunities in these fields after doing a one-year programme from IIMs or ISB; well at least it was so till the recent melt-down.
What the future holds, no one knows

.
I met a person aged about 34 years, with very good academics and excellent work experience of 12 years in well known MNCs in the IT domain and in a middle management position and he was doing 2-year PGP at one of the top-IIMs; when I asked him why he is doing a 2-year PGP rather than a one-year MBA, he said, "The brand value is better; the net-work is better and one has a chance to go deeper in the chosen specialisation and net-net, it is worth the extra year". Well these are his words; it may not necessarily apply to every one.
Regarding %s being unfair for the purpose of comparison, I don't see any unfairness. It surely is a better explanator of why there is not much difference as one would expect between the avearge pay of 2-year IIM graduates from IIM A, B & C with less experience and the avearge pay of ISB graduates with about 5 years average experience.
Secondly, even from the point of job opportunities, I believe % is more meaningful in assessing the odds of a student getting the kind of job he/she desires rather than absolute number.
Say, for the sake of explanation, if 100 students out of 500 from school-A are able to get into consulting jobs vs let us say 100 people out of 250 students get similar kind of jobs in school-B and if you are looking for a career in consulting which one would you choose!