I really think that Adobe takes pride in destroying compatiblity with 3rd party plugins with their yearly update. Would it be too hard for the SDK's to be released to 3rd parties in advance, so they have a reasonable chance to update their plugins to coincide with Adobe's version release? Every, single, year, I have to hold on to old versions of Indesign and Acrobat until the plugins are updated, months down the line. This is getting very, very, old.
It is very old, but what is the problem, really, with waiting a few months and letting other people on the bleeding edge find the bugs? Are the new releases so very enticing...? Speaking as a plugin developer who constantly finds us running on the spot rather than adding new things people want ... Acrobat by the way is constantly changed, without warning, not just annually...
SDK's are released well in advance via the Prerelease program. One can sign up for the InDesign Developer Prerelease program and get access to prerelease builds in addition to SDK's. However, many developers including me hold on to porting the plugin to the new version untill it's stable and gains decent uptake, this seems to be the case with the developer of your plugins as well.
As Manan writes, the plugin SDKs are available in advance. I got the v18 SDK and was able to re-compile my plugins on September 7. The SDK for v17 was available on September 14 of last year. In each case, though our plugin is extremely complex, recompiling was almost a formality. Make sure to sign up for the InDesign Developer Prerelease program and get access to prerelease builds in addition to SDK's.