Technically it’s a myth, but for all intents and purposes, there is truth to it.
Cecil’s answer is partly true, but any somewhat experienced wine buyer should know that all those (standard sized) wine bottles, no matter how tall or short, thin or fat, deep or shallow punt, are 750 ml.
You’ll find all kinds of facts about how the punt strengthens the bottle, and again this is partly true (it definitely does add stability to the bottle, especially while running on a bottling line), but that’s not necessarily why you’ll find a better wine in a bottle with a deeper punt.
Winemakers like to ‘showcase’ their better wines. It’s all marketing. So, a better wine is worthy of better packaging, and then, a heftier price tag.
They’ll go for the expensive, rare, European bottle, the finest grade cork, the best tin capsule with a fancy logo, the nicest looking paper stock, elaborate label design, and so on.
That fancy European bottle (that costs more) usually has a deeper punt, better coloring, less flaws in the glass, etc.
The wine industry is very slowly realizing (after the past couple of years and a major juice glut) that all the fancy packaging isn’t always necessary. So now more than ever you can find a very good wine, in less expensive packaging. When the overall cost of goods comes down, so does the consumers price (think Two Buck Chuck.)
Overall, a nice package might indicate that the wine your buying could be something special (or at least better than average), but it’s definitely not something to base your purchases on.