WGL pixel format - color bits vs alpha bits

Question

I use the following code to see available pixel formats:

const int attrib = WGL_NUMBER_PIXEL_FORMATS_ARB;
int count = 0;

if (!wglGetPixelFormatAttribivARB(dc, 0, 0, 1, &attrib, &count))
{
    return 0;
}

const int attribs[] = {
    WGL_DRAW_TO_WINDOW_ARB,
    WGL_SUPPORT_OPENGL_ARB,
    WGL_DOUBLE_BUFFER_ARB, 
    WGL_ACCELERATION_ARB, 
    WGL_PIXEL_TYPE_ARB, 
    WGL_COLOR_BITS_ARB, 
    WGL_RED_BITS_ARB, 
    WGL_GREEN_BITS_ARB, 
    WGL_BLUE_BITS_ARB, 
    WGL_ALPHA_BITS_ARB, 
    WGL_ACCUM_BITS_ARB, 
    WGL_DEPTH_BITS_ARB, 
    WGL_STENCIL_BITS_ARB, 
    WGL_AUX_BUFFERS_ARB, 
    WGL_FRAMEBUFFER_SRGB_CAPABLE_ARB
};

const int attribsCount = sizeof(attribs) / sizeof(attribs[0]);
int values[attribsCount] = { 0 };

for (int i = 0; i < count; ++i)
{
    if (!wglGetPixelFormatAttribivARB(dc, (i + 1), 0, attribsCount, attribs, values))
    {
        return 0;
    }

    //read values
}

There is a pixel format which has 32 color bits but alpha bits equals 0:

WGL_DRAW_TO_WINDOW_ARB: true
WGL_SUPPORT_OPENGL_ARB: true
WGL_DOUBLE_BUFFER_ARB: true
WGL_ACCELERATION_ARB: WGL_FULL_ACCELERATION_ARB 
WGL_PIXEL_TYPE_ARB: WGL_TYPE_RGBA_ARB 
WGL_COLOR_BITS_ARB: 32 
WGL_RED_BITS_ARB: 8 
WGL_GREEN_BITS_ARB: 8 
WGL_BLUE_BITS_ARB: 8 
WGL_ALPHA_BITS_ARB: 0 
WGL_ACCUM_BITS_ARB: 64 
WGL_DEPTH_BITS_ARB: 24 
WGL_STENCIL_BITS_ARB: 0 
WGL_AUX_BUFFERS_ARB: 8 
WGL_FRAMEBUFFER_SRGB_CAPABLE_ARB: true

How to explain that ? I have expected to see 24 color bits for the above red, green, blue and alpha bits values.