I dear say I never had issues with MS Updates in years on a various number of systems and various windows flavours. Rather, I had several issues due to updates not being installed. So, while I would try to reassure you on Win Updates, I am not going to question your fear that MS updates may break some of the system components, obviously our personal experiences may vary and generate different opinions.

Having said that: do SageTV or SlimCenter (I don't know them at all) use DirecX in some way? Or .NET? Or do they make any call to the OS DLLs or other OS components? I assume so. Then, should SageTV fail again, I suggest that you actually consider to run SageTV after another full (manual) system update.
On the same token: did you update video drivers and audio drivers? Drivers are the source of most windows system crashes.