Of course, one reason for
Betfair's sideways move into Fixed Odds business is that shareholders demand to be fed and their appetites only grow over time.
I suspect(I don't know) that Betfair executives came to realize that a betting exchange could only produce so much growth. I think they realized that punters prepared to embrace exchange betting were finite in number and that 'fresh blood' was arriving only as a trickle rather than the required torrent.
Given that Betfair over the last few years had already moved into poker, casino, games etc the Fixed Odds move was all they had left to grow the business to the degree required by institutional investors that own so much of the company.
On another note Betfair recently announced that its user base had grown by 18% in the second half of the last financial year. It would be interesting to know what proportion of this new business is ostensibly exchange business and what proportion fixed odds business, casino or poker etc. I'd personally find it difficult to believe that new and active exchange users represent more than a fraction of the new users.