Google, Amazon, Samsung, Acer, Asus, these are just a few companies that sell tablets under their own brands. There are several others.
Their number may seem great, but it really isn't, compared to the multitude of manufacturers that actually put such devices together.
Speaking of which, many white-box tablet makers will have to retire next year, as few have the resources and expertise needed to assemble slates priced at $99-150 / 99-150 Euro.
White-box means unbranded. Acer, Asus and the others don't actually manufacture the tablets themselves. They contract others to do it.
Many of these “others” will have to cut their losses soon, since the number of orders isn't exactly large enough for everyone to get a comfortable share.
On a related note, low-cost tablets will supposedly become more common next year, with Apple as the only one able to stay in the high-price tablet market.