Well, your difference in results could be a number of a things. As far as Excel is concerned, pay close attention to how many decimal places you allow in each cell. If your cell is too small, the number will be rounded up and it's possible it could be radically different from the number SPSS & MINITAB give you.
I like SPSS because the syntax editing is pretty simple. At work, I use SPSS, Excel and STATA, and honestly, I prefer STATA. It's very flexible, even if it is trickier to use.
Anyway, It's hard to answer your questio without more details. Your values can also vary if you haven't done the right command. And finally, as one person mentioned above, each program uses a different algorithm to compute the values your asking for, so your answers will probably vary slightly from time to time. However, if there are big differences, then you should check your method or your data, because something in the command you executed or missing data could be causing you problems.