No, but kits are harder to screw up.
I think Jet hit on the most poignant issue. Kit manufacturers go to great pains to:
a) select good fruit from all across the globe
b) properly store and transport it
c) expertly test it with state of the art equipment, then adjust as needed
d) prepare and package for convenient use
e) stand behind their product
In my opinion, there's NO WAY you could do this yourself for $80. It gives you access to grapes that would be unavailable to most home winemakers, or at least cost prohibitive.
For the record, I do make lots of wines from scratch too. The initial material cost is lower and sometimes I like the taste better. But when I make wines from scratch, some are good, others are "OK" and some stink. My success ratio using kits is much higher. I have "from scratch" batches that I wouldn't bring out to share with guests, but I've never had a kit wine I was hesitant to share.
If you were to do a cost analysis for the average home winemaker who makes small batches, and you factored in labor, expense, waste, materials, failures, etc. I believe your cost per bottle of a kit wine would be less that of wines made from scratch.