In DTM, _satellite.getVar will honor the "window." prefix in the first argument.
In Launch, this is not supported.
For example :
_satellite.getVar("window.digitalData.page.pageInfo.pageName")
It is fairly common practice in DTM to use the above as it will fail gracefully if any part of the nested object is undefined.
The same problem exists for "param.", "event.", "rand", and "target." prefixes
These may present migration hurdles for some DTM implementations.
The DTM to Launch Migration Assessment at https://www.searchdiscovery.com/solutions/partners/adobe/adobe-launch/dtm-launch-assessment/ presently flags these cases as issues that will need to be fixed when migrating.