If your on a decline the weight is naturally going to to pull down towards your body and your head (so effectively your body is resisting the weight from coming in a manner of contrasted upright row therefor putting some strain on the front delt.) There will be pressure on the join in both movements but there will certainly be additional strain when your balancing the weight that much more.
The muscles used during an upright row are antagonistic to muscles used in a decline bench. That is a poor example.
During decline bench press, your shoulder joint has larger muscles which play a role in shoulder stability. Therefore, it has MORE stabilization potential in decline versus flat or incline movements which rely on tiny rotator cuff muscles for stability.
In contrast to your belief concerning joint strain, the decline bench has MUCH smoother joint mechanics versus flat or incline movements. There is less strain on the joint capsule and labrum.
The decline bench press is frequently the only press that lifters with shoulder injuries can perform without pain.
It's rare that someone who is lifting with good technique would ever have shoulder issues with a decline movement, unless severe pathology was involved.