Not knowing where the calculations from your .png snapshot comes from and the assumptions behind it, I would guess that the difference between the two is that BeerSmith takes into account the thermal expansion of water at the rate in your equipment profile (4%). If I manually calculate the difference between the two values, it comes out pretty close to the 4% for thermal expansion.

If you are going to use different calculators to compare BeerSmith's calculations every time you brew, you will constantly be chasing down different numbers between them. Each program or independent calculator makes assumptions about various parameters in order to give you numbers. Beyond that, the calculations are pretty much the same. It is a common problem people have and is a distraction from furthering your goal of setting up BeerSmith to best represent your process. If this is your first time using BeerSmith, you have done well in personalizing your equipment profile. Now take the results of your actual brews and use these numbers to validate the assumptions in your equipment profile to make the program better model your results for you.