Typically, each product imports and exports the major formats. But, inevitably, some vendors decide to lock customers into their products. Their format is best, they claim, so it makes sense to deal only in their formats and ignore all others. Of course, it never works out. Users get ticked off because they cannot move their data easily from place to place.
Utilities spring up to transform one format into another.
Less prominent vendors create a standards group and produce a format that is truly open. The major players have their own map and data formats that are de facto standards. But these aren't satisfactory for users, especially those who must move data from one GIS to another, as is often the case in group or hierarchical projects. Because government agencies are probably the largest market for GISes, they will play an important role in standards setting. For example, FGDC has embraced the Content Standard for Digital Geospatial Metadata.