Re: ANTMINER S7 is available at bitmaintech.com with 4.86TH/s, 0.25J/GH
Both difficulty and global hash rate are rising... So, i think there are some new miners somewhere... and if Bitfury (or anyone) releases a x20 times more efficient miner, the actual miners will be obsolet on next day... 
It takes TIME to build and deploy new hardware. Won't happen in a month, might happen in 3-5 *IF* the efficiency gain was actually in the 5x they're CLAIMING over the now current generation gear - and even then some of the current gen might still be profitable for a while for some situations, like "wintertime space heating" or "free electric" like even the original ASIC gear is now.
I suspect the last couple of diff increases have been fed mostly by (1) Bitmain making S7s to swap in place for their own farm S5s, then (2) those S5's being sold as "used" and being brought online, more than the fairly FEW sales of the S5+ they had. I find in interesting that the "available" PICMAC contracts are still at 30k, even with quite a few thousand having been sold....
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Next: there are 3 hashboards at 400W each making the total for ~1210W.
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Not quite right. The hashboards eat less than that, then the PS (which is quoted as 93% efficiency) adds a little to the load. *IF* you are using a PS with the same efficiency, then your calculation would be correct and the final current draw from a 110V circuit would be in the ballpark you cite (exact amount would depend on the voltage at the input to YOUR powersupply, 117 VAC is a NOMINAL voltage it can commonly range 110-120 volts and sometimes down to 100ish).
In any event, any combination of Gold or better efficiency power supplies running a single S7 and nothing else should easily stay under 12A total current draw.
Unless your ambient tempertature is VERY high, you'll have plenty of reserve on a common 15 Amp US "117 VAC" outlet - I forget offhand but I think the National Electric Code cites current capasities at something like 50c before requiring derating, but would have to go back and reread it to be sure.
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When S7 release it has more than 12 months BEP (include tax)
Actually, it's BEP per your stated method of calculation of the S7 at release was a little over 8 months, NOT 1 year.
I came up with an estimate that it would be 4 BTC before release based on a 250 day BEP, but that was assuming 2 hash boards 2 strings and therefore a little less than half the TH at a little less than half the power at a BTC price when I made the estimate of a hair more than the release date - given the actual figures, it should have been released at more like 8.5 BTC for a 250 day BEP. (Bitmain appears to assume appx. 10 cent / KWH on their version of your BEP calculation).
I have ZERO CLUE where you are comming up with that "1 year" figure for it, that's not even close given your base assumptions on the calculation unless your electric rate used is quite a bit HIGHER than 10 cents / KWH.
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fits the economic theory-which monopolist ever reduced prices?
Standard Oil did quite a few times in many circumstances during it's "monopolistic" days.
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I am surprised that there is no second chinese company at par with BM
Lktec actually announced THEIR upcomming 5TH miner before the S7 or the BM1385 was announced.
On the other hand, it seems that a lot of the folks that were part of the last 2 gens of ASIC competition have decided to quit selling to end users.
In some cases like KnC, NO BIG LOSS. In others, sad but not suprising as Bitcoin Mining has hit the big times and greatly gone industrial since then.
Welcome to the situation of the "family farmer" over the course of this past century, but like most "tech" related thing the generations are a LOT shorter and time goes by a lot faster.
If you want to compete with the bit industrial farms, you have to be SMART and you have to play the angles, not just assume you can keep going like Granddad did and still make a living with inefficient methodology.