For what it's worth... I can't comment (yet) on why the builds aren't in the "release" PPA. However, I can offer this...
The "stable" PPA can really be thought of as 'testing'; it's a nightly build of the release version plus any new commits for that point release. Once stability has been confirmed, the "stable" version then becomes the new "release" version.
What that means here is that the release version is 4.0.8 (which is missing); by contrast, the stable version is 4.0.8-3, which means it's three commits ahead of 4.0.8 at the moment. If you wish, you can thus install the stable release instead, as that's kind of a pre-release for 4.0.9. You can see the differences between the two builds (i.e. what those three [as of now] commits are) here:
https://github.com/tvheadend/tvheadend/compare/v4.0.8...release/4.0
And yes, there's an i386 Trusty .deb in that PPA:
http://apt.tvheadend.org/stable/pool/main/t/tvheadend/