If you say so; after all, the Shuttle is the most capable and versatile launch system ever built. But commercial launches, and steadily improving Soyuz and Shenzen spacecraft, would eventually overtake it in terms of cost-effectiveness. I'd say that starting around 2012-2015, astronauts would start using another launch system (perhaps with SpaceX technology, like COTS) for reaching the ISS simply because it's cheaper than the Shuttle, but the Shuttle would still be used for construction of space stations and satellite repair/recovery, maybe until 2020 or 2025.
Well, the thing is that none of the current commercial systems started development until after STS-107 (there was formerly one that had begun earlier, but it has gone out of business). This was at least partially because Bush announced that the Shuttle was going to be retired, so there was obviously a market opening up. Without that, there is much less incentive, since the possible commercial crew markets are going to be a lot more speculative. NASA is almost certainly going to moot Shuttle replacements during that time, like the Orbital Space Plane program before Columbia, but ultimately it's cheaper in the short term to keep a program going rather than replace it. So it's quite plausible that they just keep soldiering on into the 2020s with no replacement.
Also, Shuttle has the ability to basically fly 2 1/2 missions in one; it can carry a rotation crew, plus supplies, plus bring back stuff to Earth. It would take two Dragon flights to even come close to duplicating that, so it might turn out to be cheaper to fly X Shuttle flights than 2X non-Shuttle flights (even ignoring ATV, HTV, and Soyuz/Progress).
There's some truth to that. If (a few) people protested the launch of the Cassini spacecraft

rolleyes

then there would probably be a huge uproar to a nuke-powered spaceship.
Yeah, and it's likely to come in during the development stage. Like I said, it was also one hella expensive mission; the wind-up report estimated a cost of $16 billion,
not including launch (that was estimated at another $5 billion for a three-launch scenario).