I don't see it as complicated or know what offering a blow by blow instructions will do. there is not a lot of difference between the two.
While I'm of the mindset that people can play 4e anyway they want, grid or no grid, I will disagree with this statement.
If you decide to play 4e without a grid, you are giving up some of the precision of the game, and some powers are dependent on that precision.
As an example, let's say I have a power that does a slide 3 vs another power that does a slide 4. Without a grid, the effectiveness of the slide power is often up to DM interpretation as there is some vagueness to position (are you 3 squares away from the burning lava or 4 squares?).
So if a player says, I use my power to slide that guy 3 squares and knock him into the lava...the DMs interpretation of the position is what determines whether 3 was good enough or just not quite.
Further depending on the DMs style that slide 4 power may not be useful at all, or may be extremely useful because its such a bigger slide than the other powers in the game that the DM often lets it get away with much more.
In a grid, the effectiveness of 3 slide vs 4 slide is based on the board, either he's 3 squares to the lava or 4. Its more impartial to the DMs style.
HOWEVER (here's the big butt)...there is nothing innately wrong with that. Gridless combat can be quicker to setup, might even force the players to use imagination more, and everyone in the game may be fine with the DM's interpretation to keep the game going. Its a perfectly valid way to play.
Valid...but Different.
Grid vs Gridless is a different way to play. And the more a gameset relies of abilities that use precision (and 4e has quite a lot of these) the more different the two become.