Bicycles are hugely useful -- they were the first mode of transport that was affordable to an ordinary person (though relatively about as expensive as a car today), and didn't require feeding, shoding, tackle, or stabling. With a bike, a person could move beyond 3 miles in an hour, or get to and from a railroad station allowing for much longer commutes, visits, or recreational travel.

As of the late 19th century, horses consumed about 25% of the grain production of the US. Much of that was to provide drayage of people and goods to and from railroad stations or train yards.

The first mode of transport affordable to an ordinary person was probably an animal like a donkey or an ox, etc..

Not within an urban context, and not much elsewhere. A donkey or ox required grazing access -- which meant either owning your own land or having access to a commons, as well as a stable. Bicycles, despite many other issues, don't poop.

A horse was a major capital investment. And a donkey can't carry all that much weight -- a light adult, perhaps, but only just.

The US horse population in 1915 was 20 million, contrasting with about 100 million people. Keep in mind that most of those horses were in commercial use -- drayage, farm traction (a large combine would be drawn by 40 horses), etc.

Numbers for England/UK are harder to come by, but a Google Answers thread gives 3.3 million for late Victorian Britain, and 14 million in Europe in 1800, the latter against a human population of 203 million.

The typical person, or family, owned zero horses.

http://answers.google.com/answers/threadview?id=144565

http://www.geohive.com/earth/his_history1.aspx

Though you raise an interesting question: what was ownership of draught animals throughout time, and how did that compare with bicycle sales in, say, the US, England, France, and Germany from 1880 - 1920 or so. Keeping in mind that mass private automobile ownership wasn't really a thing until the 1950s, even in the US.