Why define a Template inside a Style in xaml, WPF? - wpf

Question

I've been wondering this ever since I started using MS's control templates examples as basis to build custom controls.
take the Label example for instance: http://msdn.microsoft.com/en-us/library/ms752327.aspx
why on earth is it defined like this:
<Style x:Key="{x:Type Label}" TargetType="Label">
<Setter Property="HorizontalContentAlignment" Value="Left" />
<Setter Property="VerticalContentAlignment" Value="Top" />
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="Label">
<Border>
<ContentPresenter HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}"
VerticalAlignment="{TemplateBinding VerticalContentAlignment}"
RecognizesAccessKey="True" />
</Border>
<ControlTemplate.Triggers>
<Trigger Property="IsEnabled" Value="false">
<Setter Property="Foreground">
<Setter.Value>
<SolidColorBrush Color="{DynamicResource DisabledForegroundColor}" />
</Setter.Value>
</Setter>
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
and not like this directly:
<ControlTemplate x:Key="{x:Type Label}" TargetType="Label">
<Border>
<ContentPresenter HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}"
VerticalAlignment="{TemplateBinding VerticalContentAlignment}"
RecognizesAccessKey="True" />
</Border>
<ControlTemplate.Triggers>
<Trigger Property="IsEnabled" Value="false">
<Setter Property="Foreground">
<Setter.Value>
<SolidColorBrush Color="{DynamicResource DisabledForegroundColor}" />
</Setter.Value>
</Setter>
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
and then called as a template directly and not through the style property?
is there a hidden reason I do not see for doing things like this? or is it just one way of doing things and that's it?
(NB: don't tell me this is because of the horizontal and vertical alignment setters! we all know those are the default values for a label and this is basically useless if you keep those values)

Answer 1

Without using a Style it's not possible to automatically assign the template to all instances of a specific control type. Setting x:Key="{x:Type Label}" for the control template does not automatically apply this template to all controls of type Label.
You can make a style apply to all buttons below the declaration in the visual tree by setting the TargetType to Button, but you can't do the same with a template, if you do not wrap it inside a Style that have a Setter for the template.
Also, note that in your example you can exchange
<Style x:Key="{x:Type Label}" TargetType="Label">
With
<Style TargetType="Label">
As the x:Key is set to the TargetType if the x:Key definition is omitted.