Using Serebii.net's EventDex, I counted how many times each event pokémon was made available from 2003 to the present. Each individual opportunity is treated different, even if the pokémon in question is identical to another event. For example, the E 4 All Manaphy event, the Nintendo World Manaphy event, and the Toys R Us Manaphy event that occurred almost concurrently in 2007 are treated as separate opportunities to get Manaphy. Spin off games that allow you to catch events are also counted, such as getting Darkrai and Deoxys in Pokémon Ranger. An additional Deoxys was added to the total to also account for the Deoxys in Omega Ruby and Alpha Sapphire. The data is shown in the graph below.
As the graph shows, that although Japan does get more events than the U.S., there isn't a ton of difference for most. For example, Mew was available 3 times in the U.S. and 5 times in Japan. The only significant difference is seen with Jirachi (3 times in the U.S. vs 14 in Japan), Shaymin (2 U.S. vs 6 Japan), and Genesect (1 U.S. vs 3 Japan). So why is there any difference at all? The answer is structure and culture. There are a lot of differences in how events are handled and received in Japan vs the U.S. Let's take Hoopa, the next event, as an example. Most likely Japanese movie goers will get a download when they reserve their ticket, and then another when they go to actually see the movie. In the U.S., that's not how it works. The event system is linked to stores, not theaters. Therefore, there is no "ticket reservation mon", just the mascot of the movie given out at a local Gamestop or Toys R Us.
There is one other aspect that creates animosity for event exclusive 'mons, and that's having to wait so long for them. People often are upset they have to "wait forever" to get those end of the Dex guys. Well, you can blame the hackers for that. Hoopa was leaked in 2013, so it does seem like forever. However, it was only officially announced YESTERDAY. If there had been no hack leak of something that wasn't planned until the movie was released, there would not have been such a long waiting period. In fact, the U.S. will likely get it this Fall/Winter. Using the spoiler time table that puts us at almost a 20 month wait since it was first leaked. If it hadn't been spoiled, and you just heard about it yesterday (like TPCi had likely planned) then it would have been only a 8 - 9 month wait. Still long, but not as long as it is thanks to spoilers. You really can't blame TPCi or Gamefreak for that.
Anyway, where does that leave us on non-event exclusive pokémon like Surfing Pikachu? Well, Japan definitely gets more than those!