Could someone explain bug 770025 to me?

[Tim Gokcen <hexetic@gmail.com>]

Could someone explain the reasoning behind bug 770025 to me?
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=770025

I'm planning to upgrade from Debian 7 to 8. Why is it necessary for 
gcc-4.9-base to force the removal of gcc-4.7-base, when these packages 
share no files in common?

In my particular situation, we have software which *must* be compiled 
using gcc-4.7. I'm a little confused by message #20 which seems to imply 
that gcc-4.7 could be reinstalled after the upgrade is complete.

Thanks,
Tim Gokcen