The fact that LastPass is able to "autochange" some sites is quite nice. The ability to autochange random sites (WordPress, JoesTackleAndBaitShop, ...) is not so much a reflection of LastPass as it is the effort to support random variations in the way sites manage passwords.
Let me give you an example... United HealthCare (myhealthonline.sutterhealth.org) has long had a broken password change interface. I accepts more characters than it actually stores. That means that LastPass CAN automatically send a 30 character password, and United Health Care accepts it, but if you try to present those same 30 characters to the their login page it silently truncates them to 20 characters (or so).
Like wise some dumb banking sites don't support a full set of characters. The result is that auto-password changing has to be dumbed down to fewer characters and shorter autogenerated passwords. And some really dumb sites require one a specific set of punctuation characters or disallow certain sequences of characters. This makes the burden of auto changing of passwords quite high to "random" sites.
Your only real argument is that WordPress is a pretty commonly used site... but I wouldn't be surprised if it has a gotcha or two. For example I have a self-hosted wordpress site, but I have security on my site that doesn't allow you to even GET to the login or password change pages if you don't present a specific cookie. There is no way LastPass (or any hacker) would be able to guess my "pre-password" so it would stand no chance to hack me - or attack or change a password on my site.
In fact, one of the leading WordPress site protection plugins implemented MY SUGGESTION that they protect sensitive pages using this technique (lots of security plugins were doing it very poorly).