I dont think it's offensive what you said.
Yes they could of targeted more high profile events, Live8 or the celebrations of the Olympic bid in Trafalgar Square. But it would've been less likely to succeed since security was extremely tight around those events and a attack would have been taken into consideration. People would have worried about gathering in large numbers for gigs or celebrating in public.
The extremeists have targeted the transport systems which essentially have little or no security against terrorism. Attacking this way is designed to install fear in people everytime they get on a bus or a train every single day, rather than just really big and rare occasions which might happen every year or so. It attacks the heart of our society rather than just a single event.
My point about indiscriminate bombing is that it was done at the rush hour, arguable the busiest possible time, when there was the opportunity for maximum media coverage and attention. It also caused severe disruption to everyone in London on that day. Blowing 200,000+ people up at Live8 would not cause the same disruption or make people as afraid I don't personally think. It would of been a bigger atrocity - but would've had less psychological impact upon the general population.
Indeed it could of being significantly worse for fatalities, or if the worst case scenario was that a biological attack happened at the same time. But the more complicated it is, the more chance there is of it being stopped or it going wrong. London was sent an extremely well timed message which might not have had the same impact upon us on any other day.
I personally think that the attacks were quite poor, they weren't clever or well orchestrated. Hijacking planes and flying them for miles to crash them into high profile targets is clever and well planned, takes more execution to carry out. Simply blowing yourself or something up on a train or bus is pretty dumb-skulled.
Thats my perspective anyway.