Amazon recently celebrated the fourth birthday of its app store, but its fight for relevancy among competitors like Apple and Google is far from over. TheStreet reporter Rebecca Borison details the challenges Amazon's app store faces -- like the low reach its devices have in the tablet and smartphone markets and the fact that users of Apple devices can't reach the Amazon app store. Borison explains how Amazon is working to combat these challenges, like offering incentives as it did when it celebrated its recent birthday and gave away a bundle of 34 apps for free to consumers. But, Borison warns that the Amazon has a long road ahead before it will become a significant player in the app store ecosystem.