I recently saw this on another site, and it does seem that journalists started to remove that comma to save newspaper space although I had learned to separate each entity with a comma and that is what I do unless there is a relationship there between the final two items listed.

Another point from this other site was that when you have a legal document that states:  "I leave my estate to be divided amongst Joe, Mary, Alice and John", legally Joe would get 1/3, Mary would get 1/3, and Alice and John would split the final 1/3.  If it was written WITH a comma there (...Joe, Mary, Alice, and John), each person listed would receive 25%.

I suppose most of it matters if you are a journalist or an attorney!  LOL...  

Also, the computer listing someone mentions above would all be separated by commas for me unless there's a relationship (example:  Monitors and cables to the CPU, CPU and the electric power cable, mouse, and the screen-mounted microphone.

'And' is a conjunction, if you are using a comma to seperate something why use 'and' and viceversa.

In your given example, 'comma' is not needed before 'and'. Thus the answer is-sales, customer support and quality.

However, in some cases 'comma' is used before 'and'.

Observe the following sentences-

1. She went to the market and bought some fruits.

2. She went to the market, bought some fruits, and went out on a picnic with her friends.

Well, my examples are not upto the mark.

But the main difference is that the two parts of the 1st sentence are related to each other- 'going to the market' and ' buying things'. But in the 2nd sentence 'and' joins two parts that are not related to each other, I mean one can't imagine 'shopping' and 'picnic' going together.

Well my explanation is not gr8, but hope to fade your problem out to some extent.

High School English teacher