pYro_65:
Arduino is now being used in schools and other educational institutes.
As indeed they have been used ever since they were first created--by the very people who are currently developing Arduino & teaching with them on a daily basis.
By changing things in such an incompatible manner, most text books and/or tutorials developed by the institutes are now broken
A problem with which the teaching members of the development team are familiar. It is in fact part of the reason for the desire to have a stable 1.0 release which teachers & authors can build on in the new (Northern) school year and the future with a degree of stability & certainty. By making multiple incompatible changes at one time resources only need to be updated once.
The release of a non-backwards-compatible 1.0 is the software equivalent of what many people have asked for in terms of the "fix" for the hardware issue of non-regular pin spacing on the I/O connectors. When this has not been done it has been greeted much in the same way as the 1.0 release except for the opposite reason. 
Rest assured the improving of the experience of daily use of Arduino in educational situations has been the driving force behind the development and "fixes" in the release of 1.0--despite many attempts by experienced developers to distract the core team from this goal 
As Arduino has no control over these sites, if they are unattended, they will teach people the wrong way to do things.
That is indeed one possible negative outcome but is also an unavoidable one if we are to benefit from the organic growth of open source and Free software. Over time the accurate information will float to the top and things will be as they should be, as happened after the incompatible releases between 0015-0020 or so. "We will answer their questions on the forums. We will answer their questions on the mailing list. We will answer their questions in the classroom." We survived then too. Your assistance in these times are appreciated.
If provided libraries never get updated, Arduino starts loosing features previously taken for granted by novice programmers.
That is also a risk. Given what has happened in the past if a feature is really desired then someone will step up, make the fix, argue with the chorus then release an updated library to the acclaim of thousands*.
*Or one but that's what counts.
Your time on such an endeavour is also likely to be appreciated.
These things in my opinion could be harmful to an open source project.
They can indeed be harmful but my hope is that all of us in the Arduino community will continue to step up to ensure harm is minimised while blinking LEDs and whirring servos are maximised!
The way things look, are we to assume that 1.0 may be ditched because the upcoming 'Arduino Due' can do things more efficiently than 1.0 can provide?
No. While I do not speak for the Arduino development team they were certainly aware of the Due's existence during the development of 1.0 and its stated aim of intended stability.
While your concern for the well-being of the Arduino ecosystem is appreciated I do not yet see Massimo playing his fiddle while the magic smoke rises from a pile of ATmega328s...
--Philip;