On Wednesday, they played in Atlanta, where the Hawks were fighting for a playoff berth and where fans fight with empty seats for numerical superiority. Last week, they were in Washington on the night the Wizards clinched a playoff berth, and the crowd was less than a sellout and less than loud. But the Celtics, with 55 losses in tow, returned home to a sellout for last night’s visit by the Charlotte Bobcats, a team that trails the C’s 17-10 in the championships-to-years-in-existence count. The Bobcats are coached by Vermont native Steve Clifford, who is a great guy with a lot of friends. But these weren’t all his people filling the Garden. The Celts sold out the Philadelphia game last Friday and the building will be sold out again for the final game of their season next Wednesday against Washington. And they appreciate it. “All day long,” said Rajon Rondo. “Every day of the week.” The support the Celtics receive would be admirable in its own right. Heading into last night’s game, they were playing to 97.1 percent of their 18,624-seat capacity. So they were tied for the third-worst record in the league and had the 11th-best attendance relative to their arena size. Boston can’t promise 70 degrees in January, but it can promise a warm welcome in the Garden. “I know that would be a big reason why you wouldn’t want to leave a city like Boston,” said Rondo, “because every night, even with the season we’re having, we’re probably still leading the league in attendance or at least up near the top. “I mean, the fans in Boston, they know the game. You can’t cheat the fans. They know the game. It’s fun to play there. It’s definitely something you appreciate even more once you go on the road and see other teams that have like 6,000 people in the stands. Every night, it’s 18,000 in Boston. “So you don’t take that for granted,” Rondo said. “I know I don’t. I’ve been in the league for eight years, and in Boston the crowd is consistent. They’re always there.” It may sound a little sappy, but trust us: this is something that hasn’t gone unnoticed around the league. Joel Anthony came here from Miami, where the fans are perhaps most noted for walking out early on Game 6 of last year’s NBA Finals and missing the Heat comeback. He didn’t have anything bad to say about the Florida crowds, but he’s not shocked at all by what he’s seen here.