I suppose that depends on the solver. The documentation of the "step" function describes in the "More About/Algorithms" section, that the sample time is chose automatically, fixed step if I remember correctly. In Simulink however, you might have used a variable step solver (probably ode45), which is more accurate generally. You can also execute the "step" function with a specified sample time, try a really small sample time as 1e-6 or 1e-7 as this should increase the accuracy. The command then would be:
t = 0:1e-6:10;
For the documentation on the step function, execute the following command:
Does this yield more accurate results?
Kind regards, Stefan