Yep. I worked at Ccity and Best Buy and here is the breakdown of those stores:
Computers - Little to no profit
Printers - no profit
Videogames (hardware and software) - Little to no Profit, a loss on systems
MP3 players - Little to no profit
CDs/DVDs - Little to no profit
Digital Cameras - very little profit
The items above are all things to get you into the store to look around.
Computer accessories - PROFIT
Printer accessories - PROFIT (not so much on ink but on cables)
Videogame accessories - PROFIT
Mp3 player Accessories - PROFIT
Digital Camera accessories - PROFIT
TVs and Audio equipment is a little different. TV and Audio always make large profits, especially audio. TV and Audio accessories make a TON of profit.
Service plans, sometimes they are worth it, but they make a lot of profit too.
Computer services like Firedog or Geeksquad - Depends. If you are tech savvy, you will say ripoff, but you'd be surprised how many customers love that service.
They actually don't see a ton of profit either despite what people think. Yes, its profitable for the in-store stuff (sometimes) but when you also factor in what the techs get paid (especially the in-home technician at Circuit City when it existed and the double agent at best buy) the inhome services don't make a lot of profit in my opinion (and I worked both positions years ago so...I have an opinion

) The cost of renting the fleet vehicles (circuit citys scion or best buys beetle) and paying insurance on them alone + gas is ridiculous. I never understood why companies though the inhome service was worth it unless you are in an area that does a TON of business and the houses aren't 2 hours from the nearest store.
ANYWAY that is my experience with electronics retailers. I worked many positions at Circuit City but was only like 4 months at Best Buy then I went to work for a company overseas as in house IT lol.