They were influenced by warhammer, doesn't mean what they thought up wasn't original, which it was.
I tried to play warhammer online, but the concepts in there story was obviously very different to warcraft. I prefered warcraft due to race lore and backstory to the characters and heroes involved.
Also, if you want to presume everything rips off everything else, all genres of this nature rip off from lord of the rings.
"[Blizzard co-founder] Allen Adham hoped to obtain a license to the Warhammer universe to try to increase sales by brand recognition", Wyatt says. "Warhammer was a huge inspiration for the art-style of Warcraft, but a combination of factors, including a lack of traction on business terms and a fervent desire on the part of virtually everyone else on the development team (myself included) to control our own universe nixed any potential for a deal."
This Question has probably created the most flames wars since the dawn of the internet. No one here knows the truth but most assume that Games Workshop and Blizzard had plans for an RTS sci fi game, mostly with Warhammer content.
Games Workshop backed out of that contract leaving Blizzard with an unfinished game, they turn the tables around and finish the game, call it Starcraft and made history, yada yada.
Its not a Rippoff, of course die hard fans of GW will claim it is. :P
Its heavily, really heavily influenced by GW, just take a look.
Space Marines (Terran's) is a young race that tries to conquer the Universe and fight back the evil.
Elder (Protoss) Damn old space dude's who try to fight back the evil young races and conquer the universe for their own.
Tyranid (Zerg) Hive mind alien Race that consumes millions of worlds, both Protoss and Terran's fought them endless times.
Of course there is much more Lore to Warhammer then that, im just pointing the things out that Blizzard did. And its frickin obvious, the Terran's look like a copy of the Ultramarines, which is a chapter in the Space marines itself.
All the lawsuits won by warhammer creators and all the lawsuits lost by blizzard indicate that it is a ripoff.
The biggest problem I always have with this topic is simply there's a rather big hypocrisy with acting like Warhammer was completely original in its roots.
Any story, any game, any form of fiction whatsoever that has "Orcs" as monsterous humans is, without any exceptions, a ripoff from Tolkien. Middle-Earth is the source of the name, "Ur'uk" being the lore-based source of the name "Orc", and most almost anything that has "Elves" as "divine beings nearly identical to humans in appearance" is pulling from Tolkien as well.
The vast majority of fiction involving Elves, Dwarves, Trolls and Haflings are borrowing from Dungeons and Dragons. DnD was heavily inspired by Middle Earth. There are very few examples of "actual originality" but Middle Earth scrapes against this by taking drastically altered versions of European folklore. At least Warhammer's creators did take the time to make an extensive, and quite rich, library's worth of lore on even the anatomy of the humanoids involved, so they at least have more going for them than Warcraft did until WoW came out.
All classes to 100. Check.
Guess what. Warcraft has orcs as leaders of a faction and warhammer has "dark humans" and elves as the core features with orcs being the slaves. I cannot accept people calling wow a ripoff since they are that proud of playing a silly looking orc and constantly mock the Blood Elves who are objectively superior to every other horde race.
It was pretty much a straight rip off through WC2. Now WC is it's own thing.
When survival is the goal, it's into the spider hole!
OT; I totally agree with you OP: It'd be a rip off if they just literally copy+pasted everything and changed the names, they didn't do that.
Everything new borrows from stuff that has been successful in the past, this is how we progress. It isn't just true for games but also music, movies, novels, technology - there is no such thing as being truly original.
Perhaps at WarCraft 1, maaaaaybe at warcraft 2, but once WarCraft 3 came out, No way, WoW's story just changed itself, big time.
Howay the lads!