Entity Framework 4生成的COUNT SQL语句问题

在ADO.NET Entity Framework 4中，查询记录数的LINQ to Entities语句生成的SQL语句竟然包含子查询。

>>>使用Entity Framework 4的查询代码：

using (SpaceObjectContext context = new SpaceObjectContext())
{
    return context.SiteMsgs.Count(msg => msg.SenderSpaceUserId == 1);
}

>>>生成的SQL语句：

SELECT 
[GroupBy1].[A1] AS [C1]
FROM ( SELECT 
    COUNT(1) AS [A1]
    FROM [dbo].[club_Message] AS [Extent1]
    WHERE 1 = [Extent1].[SenderID]
)  AS [GroupBy1]

LINQ to SQL却不存在这个问题：

>>>使用LINQ to SQL的查询：

using(club_CNBlogsDataContext context = new club_CNBlogsDataContext())
{
    return context.club_Messages.Count(msg => msg.SenderID == 1);
}

>>>生成的SQL语句：

exec sp_executesql N'SELECT COUNT(*) AS [value]
FROM [dbo].[club_Message] AS [t0]
WHERE [t0].[SenderID] = @p0',N'@p0 int',@p0=1