If I hadn't played WC3 for over 4 years I wouldn't have picked up WoW in 2007. MMORPG sounded interesting, but WarCraft RPG was really what got me into it. Using the same icons as in WC3 made it just so much better. I like the WoW (or Blizzard in general) icons so much more than in other MMOs where you might play a class and all your buttons are red, because you're a warrior. One thing that really annoys me is that Blizz changed the icons of Divine Shiled after all these years. Just doesn't feel right.
Blizzard always kept things you remebered from WC3 very similar in WoW. So you didn't need an extra hint to tell you what it is. You could always tell the references. Finding the places from the WarCraft campagin or even the skirmish/mp maps(!) was one of the best things I did in my first year(s) of WoW.