Watch who you are calling crazy. People in glass houses and all that.
Walmart jumped into groceries in 2001, and overnight became the largest grocer. They now (2 years later) have a 15% market share in groceries. Cite: http://www.forbes.com/resourceful/technology/2003/06/30/cz_mt_0630walmart.html
Walmart has been doing consumer goods for much longer, and is much better at it. The company I knew about had 25% of its goods sold to walmart. That was 5 years ago. I’d have to assume that share is much higher now, probably around 50%.
Just look at the revenue: (cite: http://finance.yahoo.com/q/co?s=WMT and http://finance.yahoo.com/q/co?s=S)
Walmart: 247 Billion
Target: 44 Billion
Costco: 43 Billion
Sears: 41 Billion
JCPenney: 32 Billion
KMart: 31 Billion
I think you’d agree these are the 5 biggest competitors, right? 5 competitors total revenue: 191 Billion. Walmart is 25% bigger that all 5 combined. Take out groceries (not completely fair - Costco and KMart are big into groceries, Target to a lesser extent) and Walmart is still bigger than the 5 combined.
Then look at revenue growth - Walmart is the king, Costco and Target are the only ones close, everything else is pretty stagnant. You have to guess at KMart and JCPenney, but I doubt either of their revenue growth is better than Sears.