Ah, but what goes into your digestive system also goes into the bloodstream, and that is why. (The male one is a 'defilement' before haveing the sacrament.) I think it is the respect we have for taking the very body and blood of Christ into our bodies that means there are times when it is inappropriate for taking Communion - and not just at times when one has certain bodily functions happening, but also if one is not spiritually in the right state. We have a lot of preparation before Communion - reading of certain canons and akathists, fasting etc, and take it very seriously (at least I hope I do, but I am probably a great sinner in this respect - nor do I wish to suggest that you don't take it seriously either Bluetoria, as I am sure you do!)
I would imagine with the Tsarevich, since it was internal bleeding mostly, it wouldn't have been a problem. Maybe if he had Communion whilst bleeding externally, they would have probably disposed of the bandages or whatever else, in an appropriate manner.