Big followers

Speaking of Apple, Google, Microsoft's rat race in this nearest years, they all followed each other to involve in multiple business and became huge rivals to each other. In my research, what is interesting is that they all competing in Mobile OS, Desktop OS, cellphone, web browser, etc. Once one of them enter a new field, others would follow it too. The other interesting point is that the followers have always surpass the original dominator. For instance, Microsoft was leading th e web browser market. However, Apple's Sofari and Google's Chrome are chasing market shares rapidly.