meaning & behaviour of "Replaces" in debs

["j.j.fishbat@gmail.com" <j.j.fishbat@gmail.com>]

Hi all

On my debian/testing machine I have a 3rd party package
gerris-snapshot (the debian gerris package is very old).
And ...

  > apt-cache show libgsl0-dev

  Package: libgsl0-dev
  :
  Version: 1.11-2
  :
  Depends: libgsl0ldbl (= 1.11-2)

  > apt-cache show libgsl0ldbl

  Version: 1.11-2
  Replaces: gsl, libgsl0 (<= 1.9-4)
  :
  Conflicts: gsl, libgsl0

  > apt-cache show gerris-snapshot

  Package: gerris-snapshot
  Version: 1.2.0-080705
  Depends: libc6-dev | libc-dev, libgts-snapshot-dev (>= 0.7.6),
  pkg-config, gcc, sed, gawk, m4, proj, libnetcdf3, libgsl0

so that if I want to use the GSL development library

  > sudo apt-get install libgsl0-dev libgsl0ldbl
  Reading package lists... Done
  Building dependency tree
  Reading state information... Done
  The following packages will be REMOVED
    gerris-snapshot gfsview-snapshot libgsl0 vfplot
  The following NEW packages will be installed

The author of the package is prepared to replace its dependancies
by

  Depends: libc6-dev | libc-dev, libgts-snapshot-dev (>= 0.7.6),
  pkg-config, gcc, sed, gawk, m4, proj, libnetcdf3, libgsl0 |
libgsl0ldbl

but queries why this should be necessary -- if  libgsl0ldbl
replaces libgsl0 then shouldn't the package libgsl0ldbl suffice to
satisfy gerris-snapshot's dependancy on libgsl0?

If not, would I be foolish to ask for this as a feature request?

Thanks in advance!

Jim