Huge hit for the vendors. And possibly a bigger issue:
If the gov goes after the major suppliers through mail routes they don't have to spend any of the resources investigating or launching court cases against the individuals.
For argument's sake, is it illegal for someone to ship a package to the United States with products originating from Cuba? If I understand what the articles say, the contents were clearly declared as cigars. Their actions were open and notorious in the sense they weren't attempting to defraud the government or disguise the contents. Would it not be more likely for the government to succeed in going after the American citizen who was purchasing contraband materials?
Except under a very limited and controlled set of circumstances, under the embargo no US Citizen is permitted to purchase Cuban products (including cigars) regardless where the items were purchased. Cuban cigars are therefore considered "contraband" and subject to seizure. I'm sure there will not be an awful lot of traction in other countries to enforce the US embargo, however - once those items cross into US territory - well - there's now the O'Hare Airport story to illustrate the government's diligence in enforcing the embargo...
"Defrauding" or "disguising the contents" of the shipments is not what led to the confiscation. Regardless of how the package was marked, the contents are still "contraband". It would be akin to shipping marijuana, openly marking the package as such and arguing the shipment would now be legitimate for the same reasons you stated. I'm quite certain a judge might give high marks for effort and ingenuity, but would not be otherwise swayed.