Every datacom box supplier is developing DPI features for their products. The main driver is not targeted marketing, but QoS. When you're able to identify traffic on the application layer, it gives you a lot of extra options in determining how to route the traffic.
This way you can decide to route P2P traffic flows on best effort basis, but "over-the-top" video (eg. Youtube) flows you route through a higher quality connection. This improves user satisfaction.
That's the idea anyway, saying it's for targeted advertising sounds quite paranoid to me.