Will Robertson wrote:
> 
> True. Perhaps a better idea, for those interested in absolute
> backwards compatibility, is a (standard) method to keep the old
> package versions lying around with standardised filenames (say,
> siunitx-20080823.sty) that can be loaded when necessary.
> 
> Lance Carnes wrote about this sort of thing in an editorial in the
> most recent PracTeX Journal. So I guess there must be *some* need for
> it...

At least for the kernel and associated tools, everything is in a version
control system.  So it is not really that hard to get hold of a given
version if one needs to.  The problem of versions mainly applies to
other packages, and that is very much down to the package authors (as
was discussed at length on c.t.t recently).
-- 
Joseph Wright