My question concerns protocol for the following situation.

A male employee (single) accompanied the president of a small
corporation on a business trip to a home office of an insurance
company.  The male employee, who is also a personal friend of the
president of the small corp.(insurance agency)decided that he should
purchase 4 tickets to a special football game to be held a month and a
half from the time of purchase of the tickets.  He invited his
boss/employer/friend, the marketing director of the insurance company
(whom he knows only through business and has met twice, and the
marketing directors wife.  It was to be a gift for their anniversary
as they had both attended the college where the game was to be held.
This employee chose not to invite the wife of his employer/friend whom
he also knows very well as he has been invited to their home many
times for holidays and other occasions.  This employee says that since
he knew that the wife of his boss/friend was not a big fan of
football, he didn't think that it was necessary to mention it to her
or to invite her or even to inform her of this event and ask her ahead
of time whether or not she would like to attend.

He insists that he is correct in this and that he kept this invitation
and event secret until a day before the event does not matter.  The
day of the game, the president of the insurance agency/employer/friend
called the male employee to find out what time the game began and
mentioned that he would have to get home right after the game as he
had plans with his wife.  The male employee then asked if his wife
would like to go to this game as he had two tickets left.
Is this proper business etiquette, not to give the wife of the
president/employer/friend a chance to accept or decline this
invitation or is this considered proper and within the boundaries of
protocol?

If I had been the uninvited wife, I would have felt slighted. Even if
someone does not expect me to attend an event with my husband, it
would be nice to be given the option.

I've been in a similar sort of situation: I love opera. My husband
doesn't. Several times, my mother and stepfather have bought tickets
for me to attend the opera with them. Each time, my mother asks
whether my husband would like to go.

He never goes. But he does appreciate being asked.