Yes, technically thye are all the same size, just as a not on the above, the 75 is the sidewall height as a percentage of the width, so in a 265/75 its sidewall is 198.75mm high, 75% of the width.
The reason some look bigger, is, remoulds generally come out a different size such as the simex copies, and chunky treads always look bigger than less aggressive treads, its psycological mostly.