With out getting to technical (it hurts my brain), off the top of my head Ekotrope, and Remrate are rating software and are not approved for heating load calculations, there is probably a reason why? Have you ever noticed how low the annual cooling costs are?
I also do occasional Manual J calculations with WrightSoft, even when I use all the same calculations and values Wrightsoft usually comes up with a larger load requirement. You are able to specify the infiltration in Wrightsoft and I set it at 3 ach50. The more I learn about equipment sizing it is all about the latent cooling capacity and duct design.
Anyone including me can buy Manual J software and produce a report, there software is not exclusive to Mechanical Engineers as Rating software is to raters. Until you have to be certified to do Manual J calculations you will see many conflicting reports.
I for one am excited for Resnet/ACCA/ANSI Standard 310 and the HVAC Quality Installation Commissioning Check list being implemented this should help move us in the right direction.