@Colin Mackenzie

It's true that Trademark can have various kinds of limits & complicating considerations. A key factor in judging cases, is whether "confusion" might result from an unauthorized use. If JQ Public sees your printing press product, which you have named WordPress, and the well-known website software product comes to mind, that's "confusion".

"Relatedness" of market context is important. Your printing press sounds like the Judge would see it as quite closely related to the website-software, functionally, since both are about "publishing". Being in related markets, and using a protected name, adds to the confusion.

Then too, sheer & simple public familiarity with the protected name widens the purview & scope of protection. It's pretty tough to call your printing press "Microsoft", because everyone will immediately think of the famous company built by Bill Gates. It's highly doubtful you would be able to market even, say, hand-made horse-harness, under the name Microsoft ... to the Amish in Pennsylvania ... because even they know Microsoft.

WordPress is not yet a Microsoft, in terms of the pervasiveness of their name, but it's not a farfetched comparison. As such, with a unique name that they made up just for themselves, that has become extremely well-known ... yeah, they're in a very strong position.

[How well-known? A Google search using 'wordpress' reports 5,640,000,000 results. Searching with 'microsoft' only gets 890,000,000 hits!]

Making up your own name, for your product or service, is a good thing. A name that does not otherwise exist at all, is best. Kodak, Microsoft, WordPress. Great, unique names, created just for them. Taken, Trademarked, and rock-solid.

Your product deserves the same thought & effort.