I think euros are abstract games but deserve a separate classification due to their emphasis on family or group play. This is apparent because most 2 player focused euros are more on the abstract side.
What about Chinese Checkers? Parchisi type games?
Hell, Monopoly is heavily abstracted (and or wrong) for what it portrays, but it does seem
'about' the topic in a manner that most euros do.
Well, first off (from wikipedia): "Created in India perhaps as early as 500 AD, Pachisi is subtitled
Royal Game of India because royalty played by using servants of the royal household adorned in colored-costumes as game pieces on large outdoor boards." Which is just freakin awesome.
Secondly, if Monopoly were released today, it would be classified as a euro.
Something that often goes overlooked in this discussions is aesthetic. Eurogames have a certain aesthetic as do abstract games. So do wargames for that matter. Which is actually part of the reason I don't mind answers to "What is a wargame?" to be "I know one when I see one." I'll take that quite literally.
I do think chess is the original eurogame. So I agree that it has about as much connection to the subject as your average euro.
Again, I don't think these categorizations are exclusive. An "All euros are abstracts, but not all abstracts are euros" kinda thing.
To get to the chinese checkers thing, I bet chinese checkers and parchisi were the family games of their time, and I bet at some point they did have a theme.
I think euros need to have theme to engage people, to encourage table talk and social interactions, and to give players a sense of direction and objective. If I can say 'You are a Duke/Duchess in the Lorraine Valley in the 15th century and your goal is to use your wealth to develop your land into a thriving and prestigious holding by attracting merchants, farmers, scientists, traders, workers and all the rest,' and even if the mechanisms have zero connection to the subject (rolling dice, picking up and placing tiles), just having that theme and being able to give the players some kind of direction, a seed to let their imaginations take over, is better for a lot of players than not.
In conclusion, I have no idea what I'm talking about.