Well, in that respect it is two different games. Did it irk you to spend money on DLC for FM4 when you spent it (hypothetically) on DLC for FM3?
And as others have said, no Porsche for Horizon at least to begin with. EA still holds the license, and since the new 911 is featured in the new Need for Speed, they're probably hoping that the exclusivity of it will drive sales.
I hope, once these games have been out for awhile, EA will release a sub-license to enable an expansion much like FM4. That is, if the $$ makes sense. I've heard the FM4 Porsche expansion didn't sell well, at which point it may not be worth it for Playground/T10 to fork over the money for a sub-license.
I don't like it, but I understand these decisions from a business standpoint.
Also, here are some new screen shots, and a new video with DLC info. Car packs every month starting on Day 1, and also expansion packs starting on Dec 18th.