I DIDN'T say that the team needs to allocate $4-5 million for their draft class. That's not the case since the Rams traded their high picks. Nice of you to put bogus things into my mouth.
And yes, teams do leave a buffer - usually around $3-5 million - to cover injuries, etc. Last year the Rams ended up with just over $5 million. Apparently according to you, teams go into the regular season not expecting to sign or trade for anybody else - who might just take league minimum, but sometimes take more. GMs who want to keep their jobs plan for a certain number of injuries - and yes, players on IR count against the cap. They also budget for the practice squad. They also budget for giving UDFAs signing bonuses - the more desirable the UDFA the higher the bonus - which counts against the cap even if the player does not make the 53 man roster.
I merely pointed out that the cap during the regular season is a lot more complex than the 51 top contracts that matter during the offseason, and gave some examples. I'm really not sure what bugs you about that.