There is and will be a lot more to Spriter than initially meets the eye. Spriter is not just an animating tool... The fact that you'll be able to use the actual animation data in-game instead of full frame images, as well as other game data, like action points and collision rectangles, trigger sounds, and variable changes, as well as control on the fly image swapping for characters that get new clothes, weapons etc is what really makes Spriter very different from the traditional 2d animation programs you mentioned.
It's also important to remember that (due to unavoidable injury related delays) Spriter is still in beta and missing several important features and work-flow enhancements (including to time-line manipulation) which will make it drastically more flexible, powerful, and easy to use.... Most of these features will be appearing in the upcoming beta release, and we'll continue to improve features and work flow every step of the way to releasing version 1.0 and beyond.
As far as we've read, yes, its true that the creators of Spine were early supporters of Spriter, who basically decided (during the delay in Spriter's development) that they could make a bone centered animating tool to fit their needs for the game(s) they wanted to develop faster than waiting for Spriter. This proved be a good decision in their part, and help give another option to those who had immediate needs for a game focused bone animating tool.
We're frankly glad that the game making community had the option during our above mentioned unfortunate delay, and firmly believe that there is definitely enough room for both tools in this market that Spriter's Kickstarter campaign created. We think it will become clear by the time we release 1.0 and especially in the many releases after, that they will be very different tools, and Spriter will offer some very unique features and work-flow which will make it well worth the admittedly prolonged wait.
@TeamNotion, congratulations again on your success with Super Ubi Land, and we can't wait to see what you create with Spriter.
@ the whole Scirra community,
We feel we have a similar passion to the type that spawned Construct 2, and which is clearly guiding it to become among the most flexible, accessible and fun to use game authoring systems in history. Once we get all key features added to Spriter , we intend to prove this with a strong focus on continued improvements to UI and work-flow, on top of several entirely new features we have planned.
And of course, as hopefully you all know, we are working hand in hand with Ashley to make sure that we get full, flexible, intuitive and native Spriter support for all C2 users as soon as possible. Thanks everyone for your continued patience and support. The most exciting updates are yet to come. As per an ETA, rather than miss another, I'll just give the possibly frustrating but most accurate answer of "when it's ready". Things are progressing well on both the editor and on tests so far with the next version of the plugin, but I want to keep the option open to be sure everything works as well as possible, rather than rush to meet an arbitrary deadline.