In my experience, it varies depending on which publication you're working for. I worked for one restaurant guide that would reimburse the cost of dinner for two, including a reasonably priced bottle of wine, but they didn't pay a fee for the report. Another one I worked for only paid for a meal for one, not including drinks, but they did pay a small fee for the report, so I would often dine alone when working for them.
In fact, I would often opt for a more expensive bottle of wine on the basis that I didn't mind paying the difference myself since I was getting the meal for 'free' (not really free since it was work), but only if the wine list was interesting enough to be worth exploring beyond the house wines and the meal was likely to be of a quality that deserved a superior accompaniment.
I imagine the big name newspaper columnists like Jay Rayner will get dinner for two paid, including wine, plus a decent fee for the write-up.
Local press write-ups are often subsidised by the establishment being reviewed, and are usually divvied out among the staff as a perk - they don't usually have a named restaurant critic. This is why they are so often so badly written and full of clichés like 'My companion had...'.
