I don't think Scirra is trying to offend existing/past fans and customers, they just need to entice people to continue purchasing Construct 2 until Construct 3 comes out (after all, a sudden hiccup in any income, even if they're doing really well, is not preferred).
The 50% off is a loyalty bonus to existing customers who already are enjoying the product they purchased (C2), the 100% off first year for C2 purchases is to avoid people deciding not to buy until C3 comes out.
Personally, I think it makes sense for Scirra to target new audiences more heavily, as C2 users are probably going to stay with C2 if they're happy with it, and the way Construct has been designed up until C3 has been "get as many people to buy as possible", while C3 will finally have a business reason for keeping existing users using their product (as that will lead to renewed subscriptions every year, and hence a guaranteed income).
It's a whole new audience/market for them to tap into really, but so far it looks like they'll be continuing to appeal to both audiences (past and future)
C3 is an editor-only upgrade, aside from some helpful build services, and so you're not really missing anything to stick with C2. You still get one of the best editors to make games in, and are still at the mercy of third party exporters and runtimes when trying to play said games