This has boggled me for some time (I know I sound crazy), but here's what I've established about the Running of the Leaves:
According to Pinkie Pie, the Running of the Leaves HAS to happen for the leaves to fall. This is reinforced when after the race, due to not running efficiently, Rainbow Dash and Applejack have to run through the forest again.
Ponies have a good control over the seasons and weather in Equestria, and while it's interesting how there's no special ritual for spring or summer (meaning the leaves bloom and flourish without any help), it would make sense to have an event similar to Winter Wrap-Up for autumn.
I don't know how that's really possible how two ponies can shake the leaves all by themselves since there were a lot of other ponies in the race, so for the sake of as realistic of speculation as I can do here, I'll assume that not too many ponies need to run for the leaves to actually fall.
If this was the case, it would make sense that ponies just running around normally would shake off of the leaves, but it makes me wonder if there's something magical about the path that specifically makes the leaves fall.
Assuming all of those workarounds are physically possible, what really starts to mess with my head is when I think about scale:
Do all of the leaves in Ponyville fall when the Running happens? Let's assume that there's a great physical or magical force generated that's strong enough to shake all of the leaves, even though no leaves are seen to fall outside of the immediate area.
Does the Running of the Leaves happen everywhere in Equestria? It would make sense, since there are much larger, more populous, and more popular cities in Equestria than Ponyville. If this was the case, how is it possible for every town to organize and execute an event? This is also assuming that not every town and city hold the Running of the Leaves on the same day. If this were not the case, I doubt Princess Celestia would be in Ponyville to oversee it.
What about all of the leaves outside populated areas? How do their leaves fall? Is there some kind of unmentioned weather team to clear the leaves? If this were true, it would sure need a lot ponies, considering the scale of Equestria itself.
The next hurdle here for the Running of the Leaves is cost. Obviously it's great for the Equestrian government to not have to pay for the runners to run, but there's a lot more expenses. This is assuming all of the above listed possibilities can somehow happen.
If every announcer rents a hot air balloon, and every race takes about four hours, then renting a hot air balloon for the entire duration of the race costs roughly 268 bits, or $1,000 USD. This calculation was made with v2 of a bits to USD conversion theory that I found.
If a weather team were to shake the remaining of leaves not in a town, it would take a very large team working night and day for a very long time (probably the entirety of autumn) away from their friends and family.
It would make more sense to compare the salary of a weather team member to a groundskeeper than a meteorologist, since their responsibilities are a bit more similar. For the extreme cost shaking the leaves would take, it would be much more cost-efficient to pay them this rate, too.
The average groundskeeper salary is $25,780 USD annually. This equates to $6,527 dollars for the 91 days of autumn, or about 1,865 bits.
Let's say Ponyville is about 11 square miles, an average size for a small town. If two ponies can cover 11 miles in four hours, that means they are clearing 110 miles of leaves in a 40 hour work week. This means that two weather team ponies cover 1,430 miles in the 13 weeks of autumn.
There are approximately 57.5 million square miles of land on Earth. Let's say Equestria is about 2/3 of that size, meaning it has 38,333,333 square miles of land. If 31% of that land is forest like on Earth, and about 10% is covered by ponies in towns and cities, that means the weather team would be running through 28% of Equestria's entire land mass, or 10,733,333 miles, in 91 days.
This distance would be covered by 7,506 sets of two (10,733,333/1,430), or 15,012 ponies. This is 600,048 hours of combined working and would cost Equestria $97,983,324 USD, or 27,995,235 bits, at the bare minimum. This is without the additional expenses of coordinating the races in towns and cities.
I don't think an event of such a scale and cost would simply go unmentioned. The Running of the Leaves feels like only an annual ritual that I don't think would be absolutely necessary everywhere in Equestria. Tl;dr: The wind could probably do the same job.