ControlTemplate TemplateBinding Newbie Question

Hi 

I am bit confused about TemplateBinding in a ControlTemplate and was wondering if someone can help me get things straight.

It's my understanding that a TemplateBinding allows you to reach back into the control to obtain the value for a property. 

For example in the below xaml the BorderThickness="{TemplateBinding BorderThickness} reaches into the Button control for the BorderThickness of 2.

When I remove the BorderThickness TemplateBinding the border on the button disappears.

What confuses me is that there are no such Template Bindings for Height and Width yet when I change these values on the Button control 

the Buttons size changes! 

Why does this happen even though I havn't bound Width and Height?

i.e. Width="{TemplateBinding Width} and Height="{TemplateBinding Height}

thanks in advance!

<Window x:Class="TemplatesTest.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="Window1" Height="300" Width="300">
    <Window.Resources>
        <ControlTemplate x:Key="MyButtonTemplate" TargetType="{x:Type Button}">
            <Grid>
                <Border x:Name="thisborder" CornerRadius="10" BorderBrush="{TemplateBinding BorderBrush}" Background="{TemplateBinding Background}" BorderThickness="{TemplateBinding BorderThickness}" />
                <ContentPresenter HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}" VerticalAlignment="{TemplateBinding VerticalContentAlignment}" Margin="{TemplateBinding Padding}" />
            Grid>

        ControlTemplate>
    Window.Resources>
    <Grid>
        <Button BorderThickness="2" Template="{StaticResource MyButtonTemplate}" Width="150px" Height="40px" Content="Click Me!" >

        Button>
    Grid>
Window>