I couldn't agree more, DocV. Just as you say, words like "team," "group" and "series" have more lexical weight than "lot" (a mere determiner), and can thus define the number of the verb.
As regards "team," in the Longman dictionary we can read the following:
• Team is usually followed by a singular verb:
Our team is winning.
A team of doctors works at the clinic.
• In British English, you can also use a plural verb:
Our team are winning.
A team of doctors work at the clinic.
However, DocV -- who speaks AmE -- uses the plural in sentence (5) to make clear that it is the members of the team that are wearing plaid socks (the team as a unit simply can't).
With "group" (I'm sure I've seen this in some other thread), the singular depicts the group as a whole, while the plural stresses the number (a group of us = some of us).