A 40 GH/s farm isn't much more efficient than a 10GH/s farm. A 100 GH/s farm has no real economic advantage over a 40 GH/s farm.
not necessarily true. a company could create an ASIC and keep it to itself
this will be very inefficient for making a 10ghash farm, but could be better than FPGAS for 10terrahash farms
currently the total value of bitcoin isnt large enough to attract "big players"
However they won't be able to keep it to themselves. If Bitcoin is big enough to warrant ASIC investment then someone else will make it, release it to the public and there goes that "advantage". That risk alone likely means whoever make an ASIC SHA-256 processor will release it to the public to recover their capital before being undercut.