When I type "[singular noun] and [singular noun]" in Word 2010, I find some interesting things.
Bread and butter is essential. (the auto-correction warns me of subject-verb disagreement.)
Bread and butter are essential. (OK)
A knife and fork is on the table. (OK)
A knife and fork are on the table. (OK)
The needle and thread is new. (OK)
The needle and thread are new. (OK)
Cost and revenue is directly linked. (OK)
Cost and revenue are directly linked. (OK)
I wonder how a native speaker would consider this phenomenon.