Okay, I can make a lot of assumptions, but I really need a solid answer about WHY Boston has an association with cream. This may be more of a culinary anthropological question, but I thought I'd try it here anyway. Here's what I know;
1.Boston has the highest ice cream consumption in the country.
2. Boston Cream Cake/Pie is the state pie.
3. A "regular" coffee, (one with cream and sugar) is known as a "Boston".
The last one, regarding coffee, I assume is because of the east coast tendency toward light and sweet coffee. I am going to go out on a limb and say that Dunkin' Donuts' Massachusetts origins helped popularize this SPECIFIC regional reference across the country, though I'm sure it already existed outside of the New England/Eastern Seaboard areas.
Beyond that, I'm willing to posit that New England, being rich in dairy farms, had a lot of really good cream and somehow it became associated with Boston. Conformation of this, or a correct fact-based answer would be appreciated.