That oh-so-controversial Spirits line about Tackle is a nice idea, but it only really works in the context of the story and how "Kamen Rider" is viewed in the older series. Stronger's saying that in death, she is once more a normal woman- because guess what? In the old universe, being a Kamen Rider sucks! Notice that in this scene he explicitly refers to her as Yuriko, rather than her alter ego.
Go beyond just Spirits though, and it just doesn't really hold together well, because the connotation of Kamen Rider has changed. You can't tell me Tackle is any less deserving of being a Rider than some asshole like Gai or Arc. Hell, go backwards and you wonder why V3 had the balls to call Riderman "Kamen Rider #4" and Stronger didn't think to call her #8, but I think that's got more to do with V3 having already bought the X-Rider record and seeing Riderman's song on there, so he knew he'd come back and he just swiped it off of there anyway.
What's more, don't forget we're talking about comics here, and if you're going to give weight to a couple lines from Spirits, then how about the Stronger-era comic where Tackle joins the other 7 Riders as... wait for it... the 8th Rider! Yeah. I love Spirits at much as the next guy, but it's still a comic. A really, really, really good comic, but remember TV never addressed the issue, which is why it's been such a sore point for years.
I give Muraeda credit for trying to rationalize the Tackle thing, but it's still a retroactive way of trying to explain what is pretty much a glaring oversight because, as Shougo has said before, Kamen Rider is by and large still a boys' club.
...until the day I write for it! :evil3: