Back to the topic of the Buicks, the Roadmaster is definately a knockoff of the Cadillac Sixteen.
I personally think that the line between a Cadillac and a Pontiac, Buick, Chevy, etc. is way too thin. Take 1999 for instance. Cadillac got in such a rush to get the Escalade into production to compete with the Navigator that they just took a Yukon and slapped a few logos on it. While the Yukon was a good car, I think that when you are paying over $10K more, you should be getting more than a label. Same thing with the 2007 - present models. If it wasn't for the logos, I would be mistaking the Tahoe for the $20K+ Escalade every day.
The same thing is happening within the Cadillac brand alone. In 2005, you had to have a really good eye to tell the CTS from the STS. I find it just a bit ridiculous. Just my 2 cents.