From what i've read in reviews, this game's mechanics look vastly similar to that of popular indie/freeware "Battle for wesnoth".... (http://www.wesnoth.org/) I don't know which game came first but Wesnoth is around for quite some time and as far as I know, based on original ideas - did somebody ripped off someone?

http://www.mobygames.com/game/fantasy-general

As for Wesnoth
http://www.mobygames.com/game/warlords-ii-deluxe

your first link led me to a conclusion that there are similarities but not enough to call anything a ripoff, and the sources of some ideas can be traced even further than fantasy general:

http://forums.wesnoth.org/viewtopic.php?f=6&t=31950

But why Warlords? It's nothing like Wesnoth, the combat system is completely different, units can stack, it's not hexagonal, producing units takes turns, there is no experience...

I don't know, both Wesnoth and Warlords have the magical ability to bore me out of my skull, so I guess they seem similar to me.

FW is very close to FG, but feels smaller in scale and tends to put you into situations where you must do something significant every single turn to get the best rating.

Haha...

But no. I love both warlords and wesnoth, the only thing i don't like about Wesnoth is the unit carryover system, but it is a system it shares with FG and FW :P I hate replaying previous scenarios to get better starting odds in the next ones.

Ughh, Wesnoth is a copy, or, better phrased, "open-source" implementation of Warlords (1 + 2, not 3 and up) engine. In fact, this is somewhere in the dev docs.

Have you played those games? I played all, and gameplay mechanics are vastly different. It's like saying Heroes of Might and Magic are a copy of Lord of the Realms. And actually Warlords 3 are not much different than the predecessors, why "not 3 and up"?

It might recreate the engine, but these are totally different games, as CaveSoundMaster said.