Why should commercial airfields offer dispensation for weather diversions? If you are out for a jolly and the weather closes in, perhaps you should improve your forecasting abilities prior to taking-off.
If you are making a flight where there is a requirement to file a flight plan, you need to nominate at least one alternate. Prior to doing this, you need to consider various issues. Cost may well be one; opening hours; proximity to your intended destination; customs & immigration; if my intended destination's wx is below limits what is the forecast at the alternate and what navaids etc. might benefit me at that alternate......etc.
If you are not filing a Flt. Pl. does it exhonerate you from considering alternates
If you have a mechanical failure and need to divert, why should you be exempt from a runway charge? You were going to have to land somewhere! (Most large airfields now charge for use of their runway on Dep - not Arr.)
When discussing this issue locally, I suggested that rather than waiving the runway charge, waive the parking fees because therein lies the real problem if your aircraft goes tech. You had to land somewhere, however, the real accumulated cost may turn out to be the burden of parking away from your base airfield, subject repairs.