If we agree this is a desirable feature, the following patch should do it.

2015-02-10 9:13 GMT+00:00 Artur Malabarba <bruce.connor.am@gmail.com>:
> Is there any code in package.el to prevent the listing of completely
> incompatible packages?
>
> If not, would this be a desirable feature, or do we prefer to always
> display everything?
>
> Context:
> I noticed that, on Emacs 24.3, package.el will list packages that
> depend on emacs-24.4, even though they are completely uninstallable.
>
> I realise package.el has changed a lot since 24.3, but I didn't find a
> straightforward way to check if this has changed, given that there are
> no packages that depend on version > 24.4 (thus my question).