Graphics is only one of many roles the IGP can potentially play. For people who frequently transcode DVD/BD movies for iPad/iPhone/whatever, QuickSync on HD4000 is several times faster than software and GPGPU transcode while providing better quality. If games start leveraging OpenCL or other forms of heterogeneous computing such as running game physics on IGP instead of robbing bandwidth off the GPU with GPGPU or burning CPU cycles for improved response times and better power efficiency.
Graphics is only the tip of the iceberg, the obvious application. Things will get more exciting for IGPs combined with discrete GPU(s) if/when heterogeneous computing becomes more common.