What would you call your Wordpress hosting service if not "WordPress Hosting"? What would you call your Linux Hosting?
>Your allowed nominative use and/or a software license does not give you a license to title your own services with their trademarks.
Citation?
My understanding is that litmus test is whether the naming implies endorsement or "official-ness" of the offering. There is no hard and fast rule like you're claiming. It's all context dependent. So while a court may find that this causes confusion I don't see it as obvious like you seem to.
Your link, while interesting (thanks!) doesn't appear to be a good analogue. Based on my reading of that page:
Debian decided it couldn't use the Firefox logo because it didn't meet their standards for openness (as it was protected by copyright). So they included "Firefox" without the logo. Subsequently, Mozilla complained that they couldn't use the Firefox name without using all the branding in its entirety. And so... Debian rebranded Firefox (and other Mozilla software) to something else.
In other words, it was Debians policy that prevented them from using the logo, not Mozillas. That's not at all the same. And anyways, none of this was tried in court (thankfully) so it wouldn't be a precedent anyways.