I think the Ticket Office can be blamed for a lot of this shambles by the way they've handled it. SC holders not already on the CL with 8000 points or more should have been allowed to buy one each today. Then tomorrow any other SC holder plus non SC holders who've attended all the other CL games. Then on Wednesday, Cityzen card holders allowed one each. Then any left on general sale on Thursday.
By doing what they've done, they've overloaded the system and crashed it.
But you're right that whoever looks after our IT should take some responsibility as well. Systems should be volume tested under real life conditions. They won't necessarily be able to cope with extreme situations but you find out limits and manage accordingly.