Different pony collectors go about pony collecting in different ways. Some are very picky and will wait ages for just the right "minty" pony to come along. Others will buy large lots or ponies that need a lot of TLC as they enjoy taking the ponies to the "spa". Sometimes there are before and after pictures and you wouldn't recognize the ponies. I know some collectors who will search ponies out methodically completing one set at a time.
And sometimes you have collectors that collect a specific pony. It starts out normal enough with maybe a standard release of a pony, and then a baby version, and a foreign counterpart, and then maybe a MOC (mint on card) one. Before you know it you can have an "army" of one pony.
In my case I am not intentionally building a pony army; I just happen to like Fluttershy. I'm a fan of her color combination and her character on the television show. G4 has enough merchandise that it appears that I have the beginnings of a Fluttershy army but I know there are Fluttershy items out there I don't have!