Hmm..bit of a sensationalist title if I ever saw one.. anyway..
The reason people compare a 10 year old game with a GTA V is that San Andreas raised the bar. Previously we enjoyed III, Vice City (in the 3D world) and San Andreas gave us not one, but 3 cities with each city having it's own feel/weather/sky colour aesthetics. San Andreas was a title that gave us many of the things we now take for granted in a GTA such as flying a plane.
It was a land mark title. Vice City replicated the success of III and gave us some new features, new location and colour palette but San Andreas revolutionized the whole series with multiple cities, car modding, clothing that we can choose ourselves and not just preset outfits, we could get tattoos and haircuts for the first time (leading to lots of roleplaying as we could customise our character to suit our gameplay) , property purchasing was more prominent, it was the first time we could swim and explore the ocean and rivers, the collectibles for the first time had meaning related to the theme and story (tagging up turf), we could fly a plane for the first time, we could learn new fighting techniques and we could recruit other NPC's early on in the game, we could take photos for the first time, we had countryside and desert to explore for the first time, parachuting was new too as was muscle building and I consider it being set in the past a feature in itself. We also could claim back our cars at the police impound, we had girlfriends that could give us awesome gifts (if you wanted to), we could go in to a betting shop or a casino and gamble our cash away and even get in debt for the first time. We had a mountain for the first time. How many people spent hours driving RV's off mountains? It was so much fun.. Actually, it's probably the first free-roam game to give us such a mountain in such a "every day life" scenario.
So you see, San Andreas captured our imaginations like crazy back in 2004. If gave us so many "first time in a GTA" experiences that fans remember so well but a lot of us seem to forget too. It was a mammoth game at the time, in the media, amongst friends. GTA was wild an unstoppable beast back then that broke the rules, gave two fingers to society and paved the way for so many games.
This was a revolutionary post.