Kind-of, sort-of.
I consider my paid-for house a part of my retirement plan, but I don't consider it part of my net worth. That is, I am counting on selling the house /reinvesting it into a smaller, designed-just-for-me retirement home on land I already own. As such, I am planning on using the equity. Since I'm moving to a less expensive area and building a smaller house (and my expectations are moderate -- it's not that I want solid gold faucets and marble counters; rather, I want everything arranged just as I want it; for example, storage just where I want it, windows just where I want them, a shower that'll be easy to use in my old age, etc.), I expect this house will cover most of the expense of the new house.
On the other hand, I don't think to myself, "I have X amount in my 401K, Y amount in my investments, and the house is worth X." Rather, I think of the house as money that I'll continue using . . . but money that's already spent. After all, I do intend to live in the retirement house 'til the day I die.