Number of Petrol Stations in Great Britain

I have used osmconvert 0.5Z to extract all features from europe.osm.pbf using a rough GB polygon (ie excluding Northern Ireland).
This resulted in 112,392,794 records with
minlat = 49.838882,
minlon = -9.2158629,
maxlat = 61.541675
maxlon = 2.135529
which looks to be correct.

However I can only find:
4698 ‘Node’ entries with tag k=“Amenity”, v=“fuel”
847 ‘Way’ entries with Amenity v=fuel

assuming that there is no overlap of data, this gives a maximum of 5545 Petrol Stations.

According to wikipedia there were 8787 in 2010, of which I estimate under 600 are in N Ireland.

So have the remainder closed since 2010?
or am I missing something?

Any assistance appreciated.

Firstly, the OpenStreetMap data contains things that people have added to the map. For petrol stations, this is probably where people have gone out with a GPS device, and surveyed them, or traced them from aerial imagery.
There have also been some larger scale imports of geographical data into OpenStreetMap. Though AFAIK this has not happened for petrol stations in the UK. I don’t think data for petrol stations is published anywhere (under a suitable licence).
So OpenStreetMap data is incomplete. If no OpenStreetMap contributors live in, or have visited a particular area, there might not be much mapped there. And even if there are contributors in an area, they might not be interested in mapping petrol stations. Its also possible that some petrol stations are not tagged correctly for some reason.

Also, you may want to check that number from Wikipedia. It seems it is from this website, from the UK Petroleum Industry Association:
It now says 8,706 sites for 2011. Though I’m not sure exactly what that is counting - eg does it include private filling stations, on industrial sites or military bases etc? Those are probably not mapped in OSM.