"Why does 100MBaud ... as a broadband speed matter?"
Actually that's a very fair question, and the answer is that for single-user households where the "broadband" connection is used by one person at once purely for what folk traditionally call "broadband", there's not much call for much over 10Mbit (or less), other than as a silly "mine's bigger than yours is" game.
However, if you do want to be smart and use one fibre to replace all the disparate existing data+broadcast delivery mechanisms, and you want to cater for more than single-user premises, then you do need a bit more headroom than current DSL (or even VDSL or super fast 50Mbit cable) services can deliver, and 100Mbit is a nice convenient number to play with, with room for a few HDTV streams, a few phone calls, a bit of "radio", some surfing, a bit of "telecommuting", etc.
There'll still be capacity constraints somewhere else in the network, but no copper-based infrastructure is ever going to cope with that level of bandwidth to the premises, and it's unlikely that any last-century-focused proposal that retains the ridiculous distinction between delivery of data for "broadband" and delivery of data for other services (primarily multi-channel TV?) is going to make economic sense.
Freeview HD doesn't make economic sense, give it up now. Same for DAB, Freesat (Sky or non-Sky)... Sky would still have all their content rights, they just wouldn't need to pay for the satellite capacity. Sky could still own the "Sky box" in the house, it would just be connected differently, via fibre and Ethernet and a smartcard rather than via satellite and coax and a smartcard. Same principle goes for the Virgin box and the Freeview box.
Too many vested interests for it to ever really happen, but why can't we get the left hand talking to the right hand, and put somebody competent (not BT Retail, not BT wholesale, definitively not Ofcon) in charge of delivering the bits over the last mile. WIth a real universal service obligation, not a token gesture. If Openreach want to be the delivery organisation (not the organisation in charge), and they're the best value bidder, fair enough (most of the potential opposition seem even worse, e.g. Virgin).
C'mon Mandy, you could get one up on Dave here...