Websites stopped being ‘adverts’ as soon as there were enough web pages that nobody would be likely to stumble across a particular one by accident. They are the next step from an advert – somewhere to give out the more detailed sales story. But they’re not adverts in themselves.
However, they do need to have a specific function, which might be giving out the sales story and backing it up with technical information. They should not be a repository of all the information a company has available that isn’t internally confidential. Once we go down that path, it becomes increasingly more difficult to ensure visitors see what we really want them to see.
I’ve seen many examples where a concept is mentioned twice on a website: once on an important page, where it’s part of the current sales narrative; and once on an old, no-longer-relevant page such as a conference paper from years ago. Does it matter? Well, it does if Google picks up the latter to show in its results, rather than the current sales page, and visitors get sent to a page they’ll quickly leave. Hiding irrelevant or outdated content by putting it in obscure menus doesn’t help here.
Companies are often reluctant to delete outdated stuff from their website. They’re also quite happy to put stuff on the site which really isn’t part of the sales or support narrative, because, well, it’s free to do so. Both practices are driven by a ‘just in case’ attitude, and both are a mistake.