It's all about mobile capablity
Please ignore the database side of this. The current SAP suite of products is only supported by 4 DMBS vendors - IBM, Oracle, Microsoft, and SAP itself (MaxDB, which has a fairly long history as ADABAS-D to SAPDB to MaxDB, but I digress). Notice that Sybase IS NOT a supported DBMS - this according to the current PAM (Platform Availability Matrix).
SAP is in need of a way to strategically support mobile connectivity to their solution. While mobile solutions for SAP have been available for nearly a decade (back to the Palm 7, if not earlier), it's a bigger need in today's market to have a strategic mobile solution, given the expected growth rate of mobile platforms like the iPhone, Android, iPAD, etc. In fact, SAP flushed much of their internal-only mobile solution in favour of partnering a few years back; Sybase was one of these partners - http://www.sybase.com/detail?id=1065930.
I am not saying this will be easy, or that Sybase will even remain a DBMS vendor; being a development partner with SAP may however have given the latter enough understanding of Sybase's technical capability for SAP to put up the funding to lock them in. Given that the Sybase DBMS is not supported for SAP applications, neither IBM or Microsoft are likely to complain much. I think we all know how much Oracle's opinion would matter here, as well.
The comments about the UI earlier are also on target, assuming the UI for the Sybase solution is a mobile one. The creation of effective mobile UI's was an area where SAP struggled with previous generations of mobile offerings. All fits, at least to me.