Why do simscape components not use branches?

If I create my own custom component, I need to use a branch

component conduction < foundation.thermal.branch
% Conductive Heat Transfer
% This block models heat transfer in a thermal network by conduction
% through a layer of material. The rate of heat transfer is governed by
% Fourier's law and is proportional to the temperature difference, material
% thermal conductivity, area normal to the heat flow direction, and
% inversely proportional to the layer thickness.

% Copyright 2005-2016 The MathWorks, Inc.

parameters
    area      = {1e-4, 'm^2'    }; % Area
    thickness = {0.1,  'm'      }; % Thickness
    th_cond   = {401,  'W/(m*K)'}; % Thermal conductivity
end

equations
    assert(area > 0)
    assert(thickness > 0)
    assert(th_cond > 0)
    Q == T * area * th_cond / thickness;
end

This is what I think the equivalent would be in a custom component.

component customconduction 
% CustomConductive Heat Transfer

nodes %conserving ports
 Th = foundation.thermal.thermal; % H:top 
 Tc = foundation.thermal.thermal; % C:bottom
end

parameters
    area      = {1e-4, 'm^2'    }; % Area
    thickness = {0.1,  'm'      }; % Thickness
    th_cond   = {401,  'W/(m*K)'}; % Thermal conductivity
end

variables(Access=private)
 Qheat = { 0, 'J/s' };% heat flux
end

branches
 Qheat : Tc.Q -> Th.Q;
end

equations
    assert(area > 0)
    assert(thickness > 0)
    assert(th_cond > 0)
    Qheat == (Tc.T - Th.T) * area * th_cond / thickness;
end

end

Why do non custom components not need to use branches? Is this correct in the way I have written this component? The simscape documentation is lacking in examples.