A couple of people have said you can't check high-wing fuel tanks without a ladder. Can't speak for other types, but every C152 I've flown has a step on the strut so you can visually check the fuel, and indeed the top of the wings. Is this not the case on all 152's?
I've rented planes where the fuel is entered on the techlog, and I've always assumed it was purely to satisfy some legal requirement rather than being intended as a proper measurement.
How could it possible be right? Not everyone leans correctly, or indeed at all, and when doing the calculation a fixed amount is normally used. OK, it's going to be alright to see if the tanks are empty rather than full, but there's no way I would rely on it to tell me how much I was starting with.
When I fly, I start from the position that I will fill up - simple as that. Then I consider weight and balance to see whether I can actually do that or not, but I will go with the maximum amount of fuel I can take - right up to the MTOW.
Admittedly even this isn't always possible if you are flying from shorter strips, but as a general principle it makes me feel a lot more comfortable.
As for fuel gauge accuracy, well, everyone knows they don't work, so they should not be taken as any indication of the fuel contents.