Assuming you're referring to ESRI, (Environment Systems Research Institute), labeling them the 'top GIS company' is highly subjective. There are IMO many better platforms out there, open source included (see GRASS and/or QGIS). They just were lucky enough to secure some significant clients early on (USGS, USFS, USFWS, USDoI, DoD, NGS, etc.), which it turn forced all their subcontractors to adopt the same platform. Their software is bloated, cumbersome, about a decade behind emerging technologies, i.e., like Google Earth, and has a very closed architecture when it comes to integration.