To be honest it looks like the EU has messed up with this one by withdrawing the particular before the general. But law is law, there is little that can be done about it.
At least, there is some flexibility as under the MDD standards are not mandatory.
According to the MDD, only the "presumption of conformity" associated with EN 60601-2-37/A2:2005 ceases to exist on 2010-10-01. Although not directly stated, the presumption of conformity with EN 60601-1/A2:1995 should also cease to exist for diagnostic ultrasounds on the same day. To consider otherwise would create a legal precedent which cause problems as other particulars start to get withdrawn, allowing all manufacturers to ignore the 2012-06-01 date for the 3rd edition until the last particular is withdrawn, which may be many years away.
The "presumption of conformity" relieves you from having to explain how essential requirements are met. But you always have the option to not use the harmonised standard and just explain. That explanation should take into account the content of the new standard.
For EN60601-2-37:2007, about the only major technical issue I am aware of is the need to limit the temperature of the ultrasound probe in single fault condition. There are some new lines added to the accoustic output declaration table as well. But it is up to the manufacturer to make a full analysis. Ideally you should comply with these new requirements, but at least if you don't comply you have to explain why the essential requirement is still met. Risk management may help in that regard.
The crunch comes with EN 60601-1:2006, as this is a huge amount of work. One saving grace, and largely unknown part of the MDD is that interpretation of essential requirements and risk is only required to use the state of the art at the time of design, provided there are no major safety issues involved. This reference can be found at the start of the MDD (in the whereas statements). It is arguable that if there is no evidence of major safety issues at stake, the pre-existing standard should be considered adequate.
Regardless of the lower level decisions about how essential requirements are met, at least before 2010-10-01 there will be a mandatory requirement to update the technical file to reflect the change in status of the older standards (i.e. that they are not harmonised), along with a justification if the harmonised standards are not used.
To take no action would be a clear non-conformity.