Does English grammar and spelling matter?
I'm not sure if the question was intended to be rhetorical, but on the assumption that you were asking that as a genuine question, I would say that it matters for several reasons:
Firstly, because, as others here have observed, not following correct grammar and spelling can introduce ambiguities in the meaning. Even when it doesn't introduce ambiguities, incorrect spelling and grammar will look unfamiliar to most people - and that will cause people to have to do a bit more mental processing when reading - so that's likely to harm communication.
Secondly, I'd say it matters because incorrect spelling and grammar is irritating and unpleasant to read for many people. To that extent, not making the effort to use correct English is likely to be inconsiderate to your intended audience (This reason is obviously most relevant if you are writing something for public consumption; it may not matter if for example you're writing a text, intended to be read by just one close friend). There is however a balance here - there is a point where being too pedantic about minor points of grammar can itself cause irritation.
Thirdly, it matters because correct spelling and grammar represents our way of keeping the language consistent, and therefore mutually intelligible to everyone. Consider for example, that we can usually read books and articles that were written 100 years ago without any real difficulty. That's because, although English has changed a little over the last 100 years, that change is relatively small - not enough to seriously hinder understanding. I would suggest that it's largely the fact that we as a society insist on following established rules - including spelling and grammar - that keeps that rate of change of evolution of the language down to a reasonable level. If no one cared about following spelling and grammar rules, then the result would be almost certainly be that how we speak and write would change much more quickly - with the result that things written or recorded 100 years ago or even more recently may well become unintelligible to many people. I think it's obvious that the economic consequences of that would not be good!
In that context, I would say that the example you quote from the National Rail Journey Planner is very regrettable. Someone needs to be told to proof-read what gets put on their website more diligently!