Forgive me Gents, but personal opinions on the state of Heathrow isn't really the point.
The point is that Heathrow is where the big airlines run most of their transatlantic and other business routes from presently and it's lodged in the national psyche as the transport hub of London.
It's not an argument about which airport is fit for purpose, it's more a statement of fact. Like you said - LHR monopolises the routes and that's not going to change a lot in the short-term, i.e. in Silverjet's 'make or break' period.
Ironically one of the biggest benefits Silverjet ccould potentially have, is if the other big airlines shifted more of their services to Luton or STN - that way they could fight on something of a level playing field and beat BA with their overall package on comparable terms.
But then, would the other airlines, like BA, f*ck things up so gloriously if they were running out of Luton? I sense maybe not.
It's a double-edged sword for Silverjet... If BA et al stay at Heathrow, then Silverjet could make an impression with their 'new' alternative, but will the business travelers migrate en masse to Luton off their own backs? Or will they plump to stay with what they know, safe (ish) in the knowledge that BA (in theory) could get them moving should an a/c go tits up, or offer them flexibility on departure times if their own plans alter?
If BA and the gang ship some of their offering out of LHR to LUT and STN, then it could be good news for Silverjet because they could steal some of BAs crowd, who were going out to Luton anyway. But like I said before - BA might be slick from LTN, and they could just chuck some cash at it in the short-term (say, 6-18 months), which would be enough to squeeze Silverjet until they go pop. If BA move to LTN, STN or elsewhere, then they would invariably have fancy new facilities of their own... they would have to!
The big worry has to be, though, that a business traveler might only suffer a bad experience with Silverjet once and once only. What will happen if the Silverjet plane goes balls up? With all the best intentions in the world, and eternally looking for a better alternative to BA, one mis-hap with Silverjet and the delays that ensue might be enough to force a previously dis-gruntled BA convert back to BA, simply because of the volume they offer, or because the airport the operate from (i.e. Heathrow) offers more transatlantic alternatives.
Then there's BAs benefits/loyalty packages, which the bean counters at Mr Bloggs' company would need to be convinced to leave behind.