magnifiers vs relative font-sizes

Does anyone have strong reasons for preferring relative font-sizes to a screen maginifier?

if so what are they?


For magnifiers:

There is a serious conflict between the necessity of
keeping everything on one page, and allowing users to control font size.

for people with severe learning difficulties, this is particularly acute.

magnifiers, allow one to gain a feel for the whole document, whilst
enlarging a part.
setting the font size to large makes the document larger than the screen, and
one looses the ability to percieve the whole.
further, a great number of people don't appreciate that there is more than
one can see.


from an offline discussion with Boris Zbarsky, following from a recent brief thread at www-style: 
scale: font-size to % of client window?



thanks



jonathan chetwynd