Well, I think it can be more granular than merely 4 categories. There are plenty of subcategories. I can easily tell between grapes (I only drink red) and I much prefer a Bordeaux to just about anything, except maybe a really good Burgundy or Borolo or a really spicy Australia blend depending on my mood.
I figure most would be able to easily tell between a Pinot Noir and a Shiraz, and with practice, one could start to hone their skills and get into figuring out proportions in blends.
If a wine is very fruity, the nose could easily exhibit memories of raspberry, plum or cherry. For those well experienced with eating grass and dirt and sniffing leather (yes there are those that train for this), they will have a more elaborate palette because they will have learned to distinguish between various scents.
If scientifically humans tend to max out at 4 particular flavours (wood, fruit, leather and spice for instance from a wine) then those proclaiming 6-8 may be spinning a tale, but otherwise it wouldn't be too hard to get various flavours particularly as the oxygen begins to react with the wine over time.
Anyone have a quick taste upon opening and then another right after decanting and then another after letting it sit for 3 hours...well, those are all variables that will change the flavour of the wine. Also, temperature has a large effect on the taste as well.
The best advice is to taste various wines and try to stay within a company's offerings or a type (terroir and country) to get the most bang for your buck.
Those that love Merlot and may be willing to spend $50 on a bottle, may be pleasantly surprised when tasting Carmenere wine from Chile. This is very reminiscent of the Merlot grape and was actually thought to be Merlot grapes until not too long ago folks figured out it was actually the Carmenere which was thought to have been lost to wine makers a hundred years ago. A good bottle can be had for $20 and will compete handsomely with Merlots in the 50+ range.