From my understanding in Asia, the Big 4 (-KPMG + Accenture) are doing quite well here and proving to be tough competition for MBBs as well, for the following reasons:
1) Ready clientele from tax and audit functions
2) Focus on implementation as well and (vs only strategy)
This makes them a one-stop shop for various needs and makes knowledge transfer and client interaction smoother, since they would have a working history with the client and strategy recommendation takes into account knowledge which a pure management consultant / strategy consultant may not delve deep into.