I see where you are coming from, there probably is dissolved oxygen in the water to begin with and over time will slowly rise to the highest point so when it's vented the pressure must fall?. I think deaerated water is recommended when filling solar thermal systems to avoid air eventually gathering up in the roof tubes/panels which are then difficult to access for venting.
I had years of experience with what were known as heating Deaerators where the HP boiler feed water was scrubbed (mixed) with low pressure steam to get rid of any air, this was then vented through a automatic air vent but if this got blocked the deaerator temperature would start falling even though the deaerator was kept at 1 bar pressure corresponding to a (steam) temperature of 120.4C, we flagged a alarm when the water temperature fell to 115C.
I had years of experience with what were known as heating Deaerators where the HP boiler feed water was scrubbed (mixed) with low pressure steam to get rid of any air, this was then vented through a automatic air vent but if this got blocked the deaerator temperature would start falling even though the deaerator was kept at 1 bar pressure corresponding to a (steam) temperature of 120.4C, we flagged a alarm when the water temperature fell to 115C.