Sometimes not all devices are made equally to run the same software – you’d generally see a variety of versions to run smoothly across different platforms. In the case of Nokia’s S60 powered handsets, Google’s YouTube client had some very patchy availability recently. Although the official version on m.google.com was 2.2.17, others found on the Ovi Store were mixed depending on what device you’re downloading it for; ranging from versions 2.2.21 to 2.2.29. Most recently version 2.2.30 popped up on m.google.com for most devices – but there aren’t any noticeable new features to separate it from previous editions; rather it may be there to consolidate the myriad of versions that’s been left to wander rampant.
source: All About Symbian