Except the problem arises when an end user thinks they know better to hold back a package than the individual which pushed it in the first place. They may be holding it back when there is a stack upgrade, and suddenly that package no longer works.
I'm sorry but the concept that you can cherry-pick updates in the new Software Center is not up for debate. I've been with the project for years and the option to allow cherry-picking in the Software Center was a mistake to begin with. It was going to be removed with the original rewrite by Ikey, and it'll be removed by me when I rewrite the Software Center to C. It's always been problematic and there is literally no chance of it being fixed until we have a more competent package manager.
When that is the case, we may be open to adding the support back in and force upgrading excluded packages when we (maintainers) simply know better (like during stack upgrades).