Implicit styles in Application.Resources vs Window.Resources?

I was looking at this question and noticed that placing an implicit TextBlock style in Application.Resources applies that style to all TextBlocks, even those inside other controls such as Buttons, ComboBoxes, etc

<Application.Resources>
    <Style TargetType="{x:Type TextBlock}">
        <Setter Property="Foreground" Value="Blue" />
    </Style>
</Application.Resources>

Placing the implicit style in Window.Resources does not cross control template boundaries, so things like Buttons and ComboBoxes maintain their default black text.

<Window.Resources>
    <Style TargetType="{x:Type TextBlock}">
        <Setter Property="Foreground" Value="Blue" />
    </Style>
</Window.Resources>

Furthermore, adding the default style in the Application.Resources makes it so you can't overwrite that style with another implicit style.

<!-- Doesn't work if implicit style with same property is in Application.Resources -->
<ComboBox.Resources>
    <Style TargetType="{x:Type TextBlock}">
        <Setter Property="Foreground" Value="Red" />
    </Style>
</ComboBox.Resources>

My questions are:

• Why is this?

• Are there other differences between Application.Resources and Windows.Resources?

• When should use one over the other?

  I understand that Application.Resources apply to the entire application, while Window.Resources apply to the window only, however I want to know why the styles in Appli