If I were betfair I would be trying to do the same thing. The profit betfair must make from me - no way pays for the bandwidth I must chew up on their servers. If Betfair can do the same trick I do at the server end, it stop me eating up there bandwidth. I do not think there care about the odd profit from over-rounding. IMHO it all aimed at reducing bandwidth costs, just like the data charges.
Apologies to fred77, but if they eat a over-round/under-round market before it appears on the API or website, then all the bots hammering the bandwidth to try and grab this will go away. Betfair as a business reduce what must be there only significant cost - bandwidth, whilst maintaining the profit from the 5% commission.
I know I this may be a bit controversial but I think there are trying to get the balance right - keeping the liquidity that me and my bots provide but driving me away from burning up bandwidth. Anyway that the direction I will be taking my bots in. Designing low-bandwidth bots which betfair should leave alone.
My 2p worth,