I think we really need to give Sarah Michelle Gellar a break.
I remember from day 1, she was always the one promoting Buffy the vampire slayer. When it was still a new show on the WB, SMG would do magazine covers, interviews, autograph signings to not only promote BTVS, but to also promote the WB at the time. She was trying very hard to get the word out about the WB and it's shows. The president of the WB Network at the time even gave her the title "The Queen of the WB", when all her work finally paid off in Season 2 and the show became a huge hit, helping other WB shows like "7th Heaven" and "Dawson's Creek" take off.
Sarah Michelle Gellar didn't even ASK for a raise when the show became popular. The WB gave it to her and said that she deserved it. Even though everyone on the show was signed on for 5 seasons, SMG's contract expired in 1999 (after Season 3). SMG could've easily decided to leave the show then and move on to do movies because it seemed like they were working for her (I Know What You Did Last Summer, Cruel Intentions), but she renewed her contract through 2002. That was a huge commitment. If she really hated playing Buffy then she would've never renewed her contract.
Now, about her having less communication with the fans compared to others. Well think about it. Buffy is probably in 90% of the scenes. SMG has a lot of work to do on all those episodes and she probably liked to use that downtime to sleep, or spend time with her husband. In the early days of the show she would always complain about the long hours and not getting enough sleep. But she was always a good sport about it. The summer between Seasons 3 and 4 instead of going off and shooting movies like how she usually did, she took a well deserved 4 month hiatus from acting.
Sarah Michelle Gellar also wasn't the one that decided Buffy would end after Season 7, it was Joss Whedon. They both made that decision together. I don't understand why SMG gets the blame for that. And why Blame anyway? I'm glad they finally ended it. SMG and Joss both felt the show had hit it's final stride and decided to end it before it was to late, which was true.
True, Alyson Hannigan, and Nicholas Brendon also were on the show for 7 seasons and were great with the fans, but once again, they didn't play Buffy Summers, and they had a lot of down time. The only thing Alyson did was star in the American Pie movies, and Nicholas did 1 or two low budget movies, but that's it. SMG had to juggle playing a major role on a television show, trying to break into a movie career, be an A list celebrity, and trying to be nice to her fans all at once, give her a break.