a luxury good

[Fujibei]

I understood that "a luxury good" is grammatically wrong when you refer to merchandize or product items. But I came across the following examples in the papers:
1. Housing is a luxury good.
2. Airtravel has become a luxury good.
3. Fish will become a luxury good.

Please enlighten me on these.

 

[Raymott]

I understood that "a luxury good" is grammatically wrong when you refer to merchandize or product items. But I came across the following examples in the papers:
1. Housing is a luxury good.
2. Airtravel has become a luxury good.
3. Fish will become a luxury good.

Please enlighten me on these.

Why do you say "a luxury good" is grammatically wrong?
In economics, a 'good' is a common term.
Luxury good - Wikipedia, the free encyclopedia