It is a bit silly. I can see Circle Mages and Saarebas using foci that aren't weapons, specifically because they are oppressed groups. The powers that be are threatened enough by them to justify keeping even a basic weapon like a staff out of their reach. Trinkets like wands, rings and crystal balls are a lot less threatening than a 6' length of wood when a mage runs out of Mana.
Blood Mages using a clunky ritual knife as a focus is thematic, even Tevinter Mages that don't dabble in blood magic might use ornate daggers, simply because their ancestors used blood magic and sacrificed a lot of slaves doing so...
Dalish Keepers using traditional or ancestral weapons make a lot of sense. If the Elvhenen and old Dalish used blades as foci, why wouldn't the Keepers of those old traditions attempt to emulate or recreate that?
Saarebas might use their manacles as a focus, or perhaps even their mask/muzzle. Having a 'volatile' approach to magic, they might eschew foci entirely and take the risks associated with blasting enemies with unfiltered energy from the fade. Make them angry enough and they will literally punch fireballs and lightning bolts into their foes.
Hedge wizards can take a unique approach to magic. They might attempt to emulate other mages they have heard about and use the same type of tools or foci, or perhaps they can take a more personal approach. One of the advantages of being self-taught, I guess.
I get that there may need to be a need to restrict weapon types due to technical reasons. I can only hope that a future DA title uses a different design design philosophy in order to enable a greater variety of cosmetic differences between members of the same class, particularly mages, though rogues could use some love too. I'm certainly looking forward to the weapon and armor customisation in Inquisition, so if that can be improved upon even further in a future title, it would be awesome.