I'm afraid wargames is one area in which I don't see a big future for tablets. Of what use is 'portability' when I want to play a guy 6,000 miles away, viewing the battlefield on as large a monitor as I can afford and my desk will accommodate? Same for FPS games, MMOs or whatever. I just don't see the scenario you suggest at all; if people get together they do so to play miniatures or boardgames, not computer games - that's the whole point. Where are these 'competitive' settings where people would trade in their 15mm armies for tablets; where's the market? And I can PBEM or play online from wherever I am on my netbook already.
If you owned a tablet you'd have noticed that a netbook and a tablet are completely different beasts. A netbook is - in essence - a mini-computer, while a tablet is just made for playing boardgames on. All the hot games in the boardgame world are already, or are getting ported to the tablet (Carcassone, Ticket to Ride, Caylus, Ra, Small World, Kingsburg, Dominion, ...) This has attracted the attention of the cardboard wargame companies and the following games/boardgame conversions have been announced for the iPad : Across Five Aprils, Battle of the Bulge, Engage (demo-ed at GenCon 2011), Hornet Leader, Manoeuvre, Peloponnesian War, R.A.F., Soviet Dawn, The Caucasus Campaign, War Patrol, Washington's War and Waterloo.
If the traditional pc wargame companies don't watch out, they will be left in the dust - especially as since from a design pov boardgames are much more streamlined and playable than most of what gets released in pc wargame world. Bought more games for my iPad this year than I bought pc wargames.