Not convinced...
Where did the term memristance come from? Resistance is a measure of how a substance resists the flow of electrons, capacitance is a measure of charge holding capacity and inductance is a measure of current induced by mag flux (or vice versa). So what is the root for memristance? Turns out that memristor is derived from memory resistor. A nomenclature that suggests that rather than being a fundamental element it is derived or dependent on other fundamental elements.
What is new about the functionality that Williams claims, seems that HP's creation is just an alternative to something that already exists - flash. Flash is constructed from the 3 basic components and transistors, which can also be defined in terms of the 3 basic components (eg hybrid-pi model). So either the description of the memristor function is inaccurate or it appears that there is no 4th basic circuit component afterall.
A little research seems to suggest that Chua looked at R = V/I, 1/C = V/Q and L = Phi/I and decided that there must be somthing that equals Phi/Q as that combination is missing from the set. This seems to suggest that a memristor will be susceptable to influence by external magnetic fields, something that Williams doesn't appear to mention even though it would have implications for practical applications of a memristor. Or maybe Williams et al haven't actually produced a 'real' memristor...
Sounds cool but just not a new fundamental passive circuit element.