In spite of this well known rule of grammar, it's still possible to hear native speakers disregard it in everyday speech.
In fact, it's disregarded in Play the Part 2.9 :
Et quelle taille ? On a des petits paquets et des grands paquets.
and you can also torture test Google Translate and see examples such as :
as-tu des petites photos ?
as-tu des grandes photos ?
as-tu des gros cochons ?
il a des derniers mots.
ils ont des premières éditions.
le français a des faux amis.
It's a mystery to me how it decides which way to roll.
The results of numerous internet discussions over the years suggest that the rule is overly formal and not applicable in colloquial French, while others say that disregarding it is just lazy French. Some suggest that it is used in situations where the use of de might be confused with the similarly sounding, deux. As with most things formal, one would expect to see it in writing, yet the well known Le Petit Nicolas, which is formally written, disregards the rule consistently in matters of colloquial speech.
The rule is real, but it's application may not be universal, and no, it's not a regional variation.
Robert