Apple's high-end Watch Edition line. Source: Apple.

You almost have to feel bad for Apple (AAPL 0.06%). While it seems odd to express concern for the largest U.S. company (which is still growing admirably), in many ways Apple is haunted by its tremendous success. For example, every new device Apple has released this century -- the iPod, iPhone, and iPad -- sold 100 million units faster than the one before it: five-and-a-half years, four years, and two-and-a-half years, respectively. The cost of each success is increased expectations.

While it's too early to declare that streak broken with Apple Watch, it could be a tall order to sell 100 million in under 2.5 years as the device is designed as a companion item to the iPhone whereas the previous devices were stand-alone entities. But if a new report is correct, Apple might just again rise to meet those lofty expectations as the Watch appears to be outselling the iPad early in its product life cycle.

Slice has sales estimates
Research analytics company Slice Intelligence (by way of Reuters) estimates Apple had sold nearly 2.8 million Watches in the U.S. as of mid-June, a little over a month into its sales life. Compare that to the full first quarter of iPad sales, in which the company moved nearly 3.3 million units, and you can see the Watch is holding up well against Apple's current quickest-selling product.

In addition, let's not forget that the Watch did not have the full quarter of sales. The actual shipping date was April 24, over three weeks into the recorded quarter, after being made available for preorder on April 10. The iPad, on the other hand, was launched very close to the beginning of the quarter, giving a longer time for sales to accumulate. Apple also has another two weeks of sales before the quarter ends, giving the company more time to beat the 3.3 million figure.

However, it's likely the Watch has already outperformed the iPad on a unit-sales basis. Slice only reports U.S. sales, but the Watch is now being sold in roughly 15 additional countries. Larger markets including France, Germany, China (Hong Kong), Japan, and Canada were a part of Apple's initial rollout, and seven secondary markets. including Italy, Singapore, and Mexico, come online June 26.

Now let's discuss expectations
When it comes to Watch sales forecasts, Apple analysts are all over the place. An early compilation from 12 analyst firms on Business Insider resulted in a first-year sales average forecast of 13 million units sold. If one uses the median to eliminate outliers, the number increases to 13.9 million units. If Slice's data is accurate, the U.S. alone could purchase this many units in the first year.

There are some caveats, of course. Along with the potential for Slice's data to be incorrect, there's the risk the watch can't continue to grow like the iPad did. In Q3 2012 -- two full years after the launch -- Apple sold 17 million iPad units, good for an annualized growth rate of 127%. That type of growth would be difficult for any product to match, let alone an items that is intended to complement another product. As an investor, however, the key takeaway is that Slice's data hint toward a more enthusiastic reception for the Watch than many analysts have anticipated -- and that can't be a bad thing.