Steam hasn't been properly detecting AMD graphics cards for years, besides:
And a whopping 20% of these performance oriented users are using Intel graphics
Not arguing that Steam is not the most reliable of sources, but:
- Even gamers use Laptops, many to play less demanding games for example while in the wait queue for their Multiplayer game of choice. Others like myself who are blessed with slow internetz at home use it to download nice 50 GB install files for Doom (just to see there's a 12 GB patch waiting as well) to save power. And guess what: I'm explicitly telling my Laptop to use the IGP for stuff like that and not it's Radeon GPU.
- Detecting AMD cards that present themselves via driver only as "HD 7900" or similar is not the sole fault of Steam. Could they do better? Yes, but that isn't the HW survey's main objective. Besides, it's often also detecting only broad classifications on Nvidia and Intel as well - you mentioned yourself "Haswell".