B) Pekovic is outperforming Gasol this season and is five years younger. It's safe to say that Pekovic should be able to sustain his current level of play over the next several seasons, which you can't say about Gasol.
C) Gasol makes $15 million more than Pekovic this year and will be making around $5-6 million more than Pekovic next season. If they can't afford to re-sign their own guy, they definitely can't afford a guy making $20 million more between this year and next.
D) Minny doesn't "want to get rid of Williams". They know that he's their last decent trade chip (well, until Love forces his way to OKC or Houston) so they're holding out for a good starting swingman (no, not Henderson) and/or a draft pick of a quality that depends on what it's being packaged with. If they just wanted to get Williams off the payroll, he'd be gone by now.