For adults who buy and play the toy bricks, nostalgia could be the main reason; but there are no conflicts with utilizing new designs/technology to the objects of nostalgia.
One of the best examples would be the VolksWagen Beetle. V W completely re-engineered their new Beetle, while incorporating some of the styles/impressions associating to their old Beetle, ending up with great success. Had they continued with the exact same technology and style of their old Beetle, it would have proven a disaster.
Another great example would be Levis' jeans, which was originally designed for mine workers, and focusing on function only. Since then, many competitor jeans makers come to totally changed the entire culture of jeans, by revamping on the styles, fabric etc, while yet still retaining the characteristics of the good-old-jeans. Had Levis remain locked to their old, function-oriented design, they would have long disappeared from the market.
The same can be said about the Lego type toy bricks. Check out the following link for a great idea: http://www.strongniche.com.tw/news/163.html