why ?

The following revision refers to this bug:
  https://chrome-internal.googlesource.com/chromeos/overlays/chromeos-overlay/+/cdc1dba220738fa9d1600322e13d99e78463468c

commit cdc1dba220738fa9d1600322e13d99e78463468c
Author: Andrew de los Reyes <adlr@chromium.org>
Date: Thu Sep 29 23:58:25 2016

The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/overlays/chromiumos-overlay/+/72bb10111745d9fc286321567349d8189e71f4e8

commit 72bb10111745d9fc286321567349d8189e71f4e8
Author: Andrew de los Reyes <adlr@chromium.org>
Date: Thu Sep 29 23:55:04 2016

chromeos/make.defaults: Don't include ghostscript by default

If you want it, just use USE=postscript.

Also, since hplip pulls in ghostscript, don't install hplip by default.

BUG= chromium:651638 
TEST=emerge-kip -av1 cups-filters both with and w/o the other change to
make.conf (on chrome os overlay) shows postscript use flag is set off by
default.

Change-Id: I33df0972c11a1e6d11d8c8a969f6d3ebdafa58f9
Reviewed-on: https://chromium-review.googlesource.com/391136
Commit-Ready: Andrew de los Reyes <adlr@chromium.org>
Tested-by: Andrew de los Reyes <adlr@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>

[modify] https://crrev.com/72bb10111745d9fc286321567349d8189e71f4e8/profiles/targets/chromeos/make.defaults
[modify] https://crrev.com/72bb10111745d9fc286321567349d8189e71f4e8/profiles/targets/sdk/package.use
[rename] https://crrev.com/72bb10111745d9fc286321567349d8189e71f4e8/virtual/target-chromium-os/target-chromium-os-1-r55.ebuild
[modify] https://crrev.com/72bb10111745d9fc286321567349d8189e71f4e8/virtual/target-chromium-os/target-chromium-os-1.ebuild

I'll presume #1 got answered elsewhere...?

yes