the first-generation Blizzaks (and the current WS-15) had their special micropore tire compound for the first 55% of the tread compound, and the rest being all-season compound.
the newer models however (the WS-50, MZ-01 and MZ-02), have the special (tube multicell) compound for the first 55% of the tread, and a standard winter compound for the rest.
i plan to get the WS-50 when my Pirelli Winter Ice tires wear down past the point of usefulness (probably 2 more seasons).
these tires should be considered as an investment. The first time you are able to avoid an accident (by virtue of better braking and/or steering), they will have paid for themselves.