It's quite simple really. You're supposed to plan your flight before you get airborne - the fact that there's (what you believe is) a full time ATSU and an ATIS doesn't help you plan unless you telephone them, and I doubt that they'd want everyone thinking of visiting giving them a call. If you're planning a flight in your Luscombe it might be useful to know that a runway that's straight into wind is not available for some reason. Or, in the case of this NOTAM, it would be nice to know that the sloping ground can't be used before flying your helicopter there to train on it.
The definitive document for pre-flight planning is the AIP - it provides all of the information that you are likely to need. If the information in it was wrong you would be unhappy. Just because the information is of no interest to you doesn't mean no-one else is interested - or relying on it. You're right that NOTAMs are assumed to be necessary if anything in the AIP is not correct - and I can't think of a better way of planning my flights than being able to rely on the AIP and any current NOTAMs.