Yes, if you have no logos then there's nothing to link to....
To link directly to the manufacturers products page you would need to change the link in
templates/YOUR_TEMPLATE/html/com_virtuemart/productdetails/default.php around line 359
from
<div class="FlexibleProductDetailsManufacturerLogoList">
<a title="<?php echo $ManufacturerName; ?>" rev="iframe|550|650" rel="facebox" href="<?php echo $ManufacturerLink ?>"><img src="<?php echo $this->product->mf_images[0]->file_url_thumb; ?>" alt="<?php echo $ManufacturerName; ?>" /></a>
</div>
to
<div class="FlexibleProductDetailsManufacturerLogoList">
<a title="<?php echo $ManufacturerName; ?>" href="<?php JRoute::_('index.php?option=com_virtuemart&view=category&virtuemart_manufacturer_id=' . $this->product->virtuemart_manufacturer_id) ?>"><img src="<?php echo $this->product->mf_images[0]->file_url_thumb; ?>" alt="<?php echo $ManufacturerName; ?>" /></a>
</div>
Haven't tested this but you get the idea..
Cheers,
Admin