While I'll agree you need a current foreign medical when you apply for 61.75 FAA certificate, you may or may not need a current foreign medical while you're flying in the US. From the FAA website:
A person applying for a U.S. pilot certificate must submit evidence that he/she currently meets the medical licensing standards for the foreign pilot license on which the application for the pilot certificate is based (see §
61.75(f)). Some foreign CAAs enter periodic medical endorsements on their foreign pilot licenses that affect its currency (i.e., Germany, Austria, Kenya, Cyprus, Canada, Guatemala, Trinidad, Tobago, Singapore, and Sri Lanka). Therefore, if the foreign pilot license must have a medical endorsement to make it valid, an FAA medical certificate alone will not satisfy the regulations. In cases when a medical endorsement is not used, a current medical license from the person’s foreign medical examiner or a current 14 CFR part
67 medical certificate will satisfy the requirement.
So if your FAA cert is not based on a licence from one of those 10 countries, a FAA medical will keep you aloft.
And, again depending on the original country license, the 61.75 glider certificate can be just as complicated. Germany requires glider pilots to hold a medical, the FAA does not. So if the German medical of a pilot flying gliders the US on a 61.75 cert expires, they are grounded where if they held a "stand alone" cert they could still fly.
Don't forget the TSA madness.