That's the way it was announced via press release this mornning; there was no talk of acquisition or how much money was involved.
GeoIQ founder Sean Gorman (bio) uses terms like "merge" when talking about the future and notes how small GeoIQs numbers are comparied to Esri's. The goal of the change? reaching the next leve by serving a larger audience with more datasets to share and visualize.
He describes the development future (a new DC development office is in the works) this way:
The team in the development center will focus on engineering core technologies for Esri, leveraging GeoIQ’s expertise in working with open data and technology communities, as well as real time and large data analytics. The team will build projects that push the bounds of data handling and analysis of emerging dynamic data sources. ...
GeoCommons and GeoIQ customers will continue to be supported as we integrate the capabilities of ArcGIS Online and GeoIQ into a next generation platform.