For the sake of argument, suppose HD receivers cost Bell $250 and HD PVRs cost them $500. None of them can play MPEG-4 streams. If Bell has to replace, suppose, 150,000 in six months ... that could easily be $50 million out of pocket for the hardware, to say nothing of the costs of customers phoning in, sending installers and couriers, etc. And that's assuming Bell can wave a magic wand and produce 150,000 boxes in the warehouse. It is a logistical challenge of huge proportions.
Yes. Every single existing receiver which wants to continue to deliver the migrated MPEG-4 channels.
Wanna bet on the 100 NEW channels by end of 2008? And, yes, one way or the other, HD customers will pay for some/all of the technology upgrades. Bell ExpressVu has stopped being a charity.
Basically, no. Digital Standard is made up of channels the CRTC says they must carry and channels Bell can carry at almost no cost. Each of the "1" Theme packs -- Family, News & Learning, Variety, Sports, etc. are also filled with "original" specialty channels which have strict carriage rights. That's why virtually none of those channels can be bought individually.
Without belabouring the point, the approx $50 entry fee for TV service represents Digital Standard and the five Bell "1" Theme Packs -- or Shaw's Basic + Tier channels or Rogers, etc; that's about 70 channels or 100ish with (free) Canadian time-shifting. After that point, the CRTC leaves it to the market: buy one or more at your pleasure. The exception is Movie Central and TMN and their related channels which are "pay tv" and operate in a bubble of their own.
HD sits on top of all of this. Essentially, after the $50 cost of entry, that's when you have influence on what HD channels to pay for and lobby for. This is equally true for satellite and cable in Canada. Bell Expressvu, for what's worth, will never have access to the US satellite market due to long-standing "free trade" agreements between Canada and the US government "cultural" industries.