Cardcaptor Sakura fans are well aware of the differences between the ending of the manga and the anime's ending, which, while not drastic, were still significant. It's not uncommon for a manga series to have an adaptation that deviates from the source material, either.
Regardless of the exact reasons, the most notable difference between the Cardcaptor Sakura manga and anime endings are how the relationships between the characters are depicted, and the sequence of certain events. Plus, the development of some of the side characters was also left out of the anime adaptation.
In the anime, Syaoran admits his feelings for Sakura right after the final battle with Eriol. He and Sakura are awkward around each other until his mother calls him back to Hong Kong to fulfill his other duties. After Sakura finds out that he's leaving, she cries in her room -- where she inadvertently creates the Hope Card. She meets Syaoran at the airport and he gives her the bear that he made earlier in the season. It wouldn't be until the second movie that Sakura would be able to return Syaoran's feelings when she thought that the Nothing Card had removed his feelings for her.
In the manga, some time passes before Syaoran confesses his feelings to Sakura in Penguin Park, where he also tells her he has to return to Hong Kong. Sakura seeks advice from her friends and makes him a bear before she runs to meet Syaoran before his bus leaves. She chases his bus as it pulls away and is able to give him the bear and confess her feelings. The story then picks up two years later, where Syaoran returns to live in Japan, and he and Sakura pick up their relationship. This is where Clear Card Arc picks up with everyone starting middle school together, and Akiho moves to Tomoeda.
The relationship between Syaoran and Sakura being explored further isn't the only change made. After his fight with Sakura, Eriol gives her father half of his power so that Sakura can be more powerful. This is because both Fujitaka and Eriol are two halves of Clow Reed's soul. Because of this, Fujitaka is now able to see his deceased wife Nadeshiko's spirit, just like his son Touya could. The anime doesn't explain any of that situation. Also, Eriol and Kaho Mizuki begin a romantic relationship in the manga that isn't acknowledged in the anime. Plus, Rika becomes engaged to Terada, and Chiharu and Yamazaki continue their relationship together as well.
Touya and Yukito are still friends, and Touya and Yue are friendly to each other. Touya's magical abilities are slowly returning to him after giving them to Yue when Sakura wasn't strong enough to sustain his magic, and he's begun developing new abilities that he doesn't go into. Yukito is also aware of his other identity as Yue. It's implied that Touya and Yukito are boyfriends.
Many of the relationships in the manga are more fleshed out, offering an extended look at how they continue to grow and flourish. If fans of the Cardcaptor Sakura anime were curious about checking out the manga, learning more about the budding relationships is certainly a solid reason.