Oh, I'm not against semi-carry Necro when it is possible for your team lineup. But more often than not in pubs, there is better (read: harder) carry than you. Question is why do you choose Necro then? Answer is, that in pubs people disregard enemy pick/own team pick when choosing heroes. I'm not saying you should always be wardbitch as Necro, but if there is no better hero for it...
Playing without wards is like being a three-day kitten - blind and deaf.
I said he is item independent, not that he wouldn't profit from them. Even heroes like CM and Tide have very nice items to get (Blink Dagger for both, BKB for CM). Their problem is they can't really farm well so they never get them, but Necro can. You can even rush Radiance with Necro and own hard, if you get it soon enough. Thats another problem, you got to end the game soon after you get some items (Meka, Hood, Vanguard, Radiance), you need to push hard and organized (problem in pubs) or you will eventually lose to harder carry.
Yes, Krobelus (Death Prophet) and also Dark Seer (maybe even Jakiro) are all this pushing tanky style. But true INT pushing carries are only Furion and Exort Invoker.